Water Resources of Arid Areas

WATER RESOURCES OF ARID AREAS PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON WATER RESOURCES OF ARID AND SEMI ARID RE...

Author: David Stephenson | E.M. Shemang | T.R. Chaoka

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WATER RESOURCES OF ARID AREAS

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON WATER RESOURCES OF ARID AND SEMI ARID REGIONS OF AFRICA (WRASRA), AUGUST 3–6TH 2004, GABORONE, BOTSWANA

Water Resources of Arid Areas Edited by

D.Stephenson Civil Engineering Department, University of Botswana, Gaborone, Botswana E.M.Shemang & T.R.Chaoka Department of Geology, University of Botswana, Gaborone, Botswana

A.A.BALKEMA PUBLISHERS LEIDEN/LONDON/NEW YORK/PHILADELPHIA/SINGAPORE

Copyright © 2004 Taylor & Francis Group plc, London, UK All rights reserved. No part of this publication or the information contained herein may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, by photocopying, recording or otherwise, without written prior permission from the publisher. Although all care is taken to ensure the integrity and quality of this publication and the information herein, no responsibility is assumed by the publishers nor the author for any damage to property or persons as a result of operation or use of this publication and/or the information contained herein. Published by: A.A.Balkema Publishers, a member of Taylor & Francis Group plc http://www.balkema.nl/ and http://www.tandf.co.uk/ This edition published in the Taylor & Francis e-Library, 2005. “To purchase your own copy of this or any of Taylor & Francis or Routledge’s collection of thousands of eBooks please go to http://www.ebookstore.tandf.co.uk/.” ISBN 0-203-02340-4 Master e-book ISBN

ISBN 04 1535 913 9 (Print Edition)

Table of Contents Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

Preface

xii

Keynote address Sustainable water management in arid and semi-arid environments W.Kinzelbach, P.Bauer, P.Brunner & T.Siegfried

3

Theme A: Problems in obtaining hydrological and geo-hydrological data Slug tests in fractured rock formations: value, pitfalls and misinterpretations P.D.Vermeulen & G.J.van Tonder Flow simulation model performance assessment using entropy approach A.M.Ilunga & D.Stephenson Data collection experiences in water level monitoring, borehole archive and research projects in semi arid Botswana M.Magowe, T.Obakeng & P.Makobo Rainfall characteristics in semi-arid Kitui district of Kenya A.O.Opere, V.O.Awuor, S.O.Kooke & W.O.Omoto Quantification of the impact of irrigation on the aquifer under the Vaalharts Irrigation Scheme R.G.Ellington, B.H.Usher & G.J.van Tonder

21

29

36

43 60

Theme B: Groundwater recharge: natural and artificial Groundwater development—identification of artificial recharge areas in Alla, Eritrea K.S.Viswanatham, F.Tesfaslasie, M.Asmellash, A.Kumar & S.A.Drury

75

Subterraneous injection of nutrient rich groundwater to the coastal waters K.K.Balachandran & J.S.Paimpillil A new method for the estimation of episodic recharge J.Bean, G.van Tonder & I.Dennis Prioritisation of the impacts of pollutants on groundwater flow systems in South Africa I.Dennis, B.Usher & J.Pretorius Understanding problems of low recharge and low yield in boreholes: an example from Ghana A.J.E.Cobbing & J.Davies Spatial variation of groundwater recharge in semi-arid environment—Serowe, Botswana L.M.Magombedze, B.Frengstad & M.W.Lubczynski Quantification of artificial ground water recharge G.C.Mishra The architecture and application of the South African Groundwater Decision Tool I.Dennis & G.J.van Tonder The development of a groundwater management tool for the Schoonspruit dolomitic compartment B.H.Usher & S.Veltman Effects of mining and urban expansion on groundwater quality in Francistown, Botswana B.Mafa & H.Vogel In situ remediation potential for Southern African groundwater resources S.Clarke, G.Tredoux & P.Engelbrecht Coastal aquifers intrusion at semi-arid region of Turkey L.Yilmaz Evaluation of groundwater recharge rates in the Kizinga catchment in Dar es Salaam region Y.B.Mkwizu & H.H.Nkotagu

85

92 99

109

122

133 145

156

168

181

191 198

Theme C: Socio-economic aspects

KNUST experiences in capacity building in the water and sanitation sector S.N.Odai, F.O.K.Anyemedu, S.Oduro-Kwarteng & K.B.Nyarko

213

Strategic partnerships for sustainable water education and research in developing countries S.N.Odai, K.A.Andam & N.Trifunovic Assessing demand for clean and safe domestic water in eastern Zimbabwe E.Manzungu, M.Machingambi & R.Machiridza The role of supplementary irrigation for food production in a semiarid country—Palestine M.Y.Sbeih Conversion of priority water rights to proportional water permits and conflict management in the Mupfure river catchment, Zimbabwe T.Mpala Impacts of water development in arid lands of Southern Africa: socio-economic issues J.P.Msangi Institutional challenges for small towns’ water supply delivery in Ghana K.B.Nyarko Socio-economic performance of Sepeteri irrigation project in Nigeria O.O.Olubode-Awosola & E.O.Idowu

221

227

240

254

262

275

287

Theme D: Application of geophysical, GIS, and remote sensing techniques

Mapping vegetation for upscaling transpiration using highresolution optical satellite and aircraft images in Serowe, Botswana Y.A.Hussin, D.C.Chavarro, M.Lubczynski & O.Obakeng Gravity study on groundwater structure in Central Butana (Sudan) K.M.Kheiralla & A.E.Ibrahim Remote sensing and electrical resistivity studies on groundwater structure zones in Central Butana (Sudan) K.M.Kheiralla & A.E.Ibrahim Monitoring and modeling of fluxes on Kalahari—setup and strategy of the Kalahari Monitoring project. Serowe study case, Botswana M.W.Lubczynski & O.Obakeng Geoelectrical investigation for aquifer delineation in the semi-arid Chad Basin, Nigeria A.Iliya & E.M.Shemang

302

313 330

346

357

Monitoring of evapotranspiration on Kalahari, Serowe case study, Botswana O.Obakeng & M.W.Lubczynski Electro-seismic survey system S.R.Dennis, M.du Preez & G.J.van Tonder Borehole site investigations in volcanic rocks of Lolmolok area, Samburu district, Kenya J.K.Mulwa Groundwater evaluation in a complex hydrogeological environment—a GIS based approach B.Mudzingwa, J.L.Farr, R.Gumiremhete & T.Kellner Application of 2-D resistivity imaging combined with time domain electromagnetic survey to map shallower aquifers in Kunyere valley, northwest Botswana E.M.Shemang, H.Kumar & J.Ntsatsi

364

381 388

406

420

Theme E: Climate change and its impact Hydraulic studies in the design of sand dams A.S.Nzaba, H.O.Farah, T.C.Sharma & C.W.M.Sitters Designing and implementing an aircraft survey mission using highresolution digital multi-spectral camera for vegetation mapping for upscaling transpiration of Serowe, Botswana Y.A.Hussin, M.W.Lubczynski, O.Obakeng & D.C.Chavarro Relevance of groundwater interaction with surface water to the eco-hydrology of semi-arid regions J.Y.Diiwu Impacts of climate change in water resources planning and management A.Opere Turning a liability into an asset: the case for South African coalmine waters B.H.Usher & F.D.I.Hodgson Environmental hydrogeology of the dolomite aquifer in Ramotswa, Botswana M.Staudt & H.Vogel Investigation of natural enrichment processes of nitrate in soil and groundwater of semi-arid regions: case study—Botswana S.Stadler, M.von Hoyer, W.H.M.Duijnisveld, T.Himmelsbach, M.Schwiede, J.Böttcher & H.Hötzl Hydroclimatological approach to sustainable water resources management in semi arid regions of Africa U.T.Umoh

430 442

450

461

467

479

489

505

Impact of cultivation practices on multiple uses of water in the Alemaya catchment, eastern Ethiopia Y.E.Woyessa & A.T.P.Bennie Geochemical evidence and origin of salinity in the shallow basinal brine from the Makgadikgadi Pans Complexes, northeastern Botswana L.N.Molwalefhe

514

528

Theme F: Vulnerability and risk Decision support for optimal water system planning: a Wadessy case study A.A.Ilemobade & D.Stephenson The importance of constructing a correct conceptual model for an aquifer G.van Tonder, I.Dennis & D.Vermeulen Water resources development and risk assessment in mountain regions of Africa H.Scheuerlein Reliability, resilience and vulnerability for reservoir sizing and operation J.G.Ndiritu Hydrological impact of dam construction in an arid area D.Stephenson & Z.Chengeta The geochemistry of fresh water supplies in Botswana L.Molwalefhe & S.Vriend Groundwater modelling with limited data: a case study of Yobe River Basin, North East Nigeria M.Hassan, R.C.Carter & K.R.Rushton

541

551

559

572

580 589 600

Theme G: Water resources management Apple and grape vinegar application as c-source in water denitrification Ş.Aslan & A.Türkman

613

Water resources management in the National Park, central Australia E.R.Rooke Integrated water resources management and agriculture in southern Africa M.McCartney, H.Sally & A.Senzanje

623

634

Challenges for managing water resources in semi-arid areas: a case study from two rural communities in Zimbabwe F.T.Mugabe & A.Senzanje An Integrated Water Resources Management tool for Southern Africa allowing low flow estimation at ungauged sites M.J.Fry, S.S.Folwell, H.A.Houghton-Carr & Z.B.Uka Organization of water services in Malawi and strengths and weaknesses in implementing Integrated Water Resources Management (IWRM) M.Selemani Towards best water resources management practice in small town water supply system in Tanzania A.Mvungi & M.Makuya Water management in the Mauritian textile wet processing industry N.Kistamah & S.Roseunee Analysis of the microbiological situation of the quality of domestic water sources and identification of the microorganisms in them, located in the semi-arid regions of the Eastern Cape, South Africa M.Zamxaka, G.Pironcheva & N.Y.O.Muyima Dry season Kalahari sap flow measurements for tree transpiration mapping—Serowe study case, Botswana M.W.Lubczynski, A.Fregoso, W.Mapanda, C.Ziwa, M.Keeletsang, D.C.Chavarro & O.Obakeng Heavy metals and radioactivity in the groundwater of Khartoum State, Sudan A.M.Ahmed Impediments to the effective implementation of a groundwater quality Protection strategy in Botswana T.R.Chaoka, E.M.Shemang, B.F.Alemaw & O.Totolo Spatial assessment of groundwater pollution vulnerability of the Kanye wellfield in SE Botswana B.F.Alemaw, E.M.Shemang & T.R.Chaoka The effect of socio-economic activities on watershed management: the case study of Gaborone Dam catchment in Botswana G.S.Thabeng & D.B.Kemiso

Author index

643

650

661

666

678 685

693

702

707

718

725

737

Preface Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

Africa’s water resources are threatened by population growth with the resultant increase in water demand, the stresses of water use for various activities, desertification, global warming and climate change, and other interventions in the water cycle by man. These effects are more pronounced in the Arid and Semi-Arid regions of Africa in particular and the world in general. It is therefore vitally important that the water resources in Arid and Semi-Arid regions are developed and managed in a sustainable and integrated manner. Integrated management of water resources in the arid and semi-arid regions of Africa requires a spectrum of efforts from local and community stakeholders to national and transboundary river basin management. This conference aims at sharing the best practices of water use and conservation around the globe. The main objective of this conference was therefore to bring together educators, researchers, practitioners, managers, policy makers and NGO’s from Africa in particular and the world in general involved in various aspects of water resources in arid and semi arid regions. The more specific objectives of the conference were to (i) Assess the current state of the art of water resources management in arid and semi arid regions with particular emphasis on African regions. (ii) Address the future water stress due to limited water resources, population growth, increasing demand and pollution and other related risks, resulting in insufficient water supply. (iii) Promote dialog and interaction between different disciplines and professions. (iv) Forster insights into issues of global sustainable development and set concrete targets to meet the need for drinking water and water borne sanitation in arid and semi arid countries of Africa and the world in general. We received an overwhelming response to our call for papers. We received over 120 abstracts and each abstract was reviewed and more than two thirds of the abstracts were accepted. Authors were then requested to submit full text of papers. The full texts of the papers were reviewed by the conference organizing committee and 68 papers were finally accepted for conference. The papers in this book “Water Resources of Arid and Semi-Arid Regions of Africa” constitute the conference proceedings. This book is subdivided into seven sections. Section 1 deals with problems in obtaining data. Section 2 deals with groundwater recharge: natural and artificial; Section 3 deals with Socio economic aspects of water demand management; Section 4 deals with geophysical, GIS and remote sensing

techniques for groundwater exploration; Section 5 deals with climate change and its impact on water resources; Section 6 deals with vulnerability and risk assessment and Section 7 water management. This book will be of interest to researchers and practitioners in the field of surface water hydrology, groundwater hydrology, environmental engineering, agricultural engineering and earth sciences, as well as those engaged in water resources planning, development and management in arid and semi arid areas. Graduate students and those wishing to conduct research in hydrology, environmental science and engineering and water resources will find the book to be of value. Dr A.R.Tombale Permanent Secretary Ministry of Minerals, Energy and Water Resources, Botswana

Keynote address

Sustainable water management in arid and semi-arid environments W.Kinzelbach, P.Bauer, P.Brunner & T.Siegfried Institute for Hydromechanics and Water Resources Management, Swiss Federal Institute of Technology, Zurich, Switzerland Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: Scarcity of water often leads to its non-sustainable use. The globally most widely spread non-sustainable practices are overpumping of aquifers, drying up of wetlands and soil salination on irrigated land. Only with much more careful management of scarce resources sustainability in the long term can be reached. Modeling is a valuable tool in the analysis of management options and scenarios. New types of data from remote sensing, airborne geophysics, and environmental tracers to name a few allow reaching a new quality of prediction. Three field studies illustrate the points.

1 INTRODUCTION Fresh water is a scarce resource on a worldwide basis. This becomes apparent when looking at the basic items of the global freshwater balance (Postel et al., 1996). Of the 110,000km3/a of precipitation on the landmass of the earth, 50,000 are returned to the atmosphere via evapotranspiration by the planet’s natural plant cover. Another 21,000 are used by man-made ecosystems (18,000km3/a by rain fed agriculture and 3,000km3/a by irrigated agriculture). This shows that agriculture and natural vegetation are already fierce competitors for the available freshwater. Of the accessible runoff of 13,000km3/a about 4,000 are appropriated by mankind. 70% of those go into irrigated agriculture. This means that a global water crisis would above all be a global crisis in food production. Compared to the 13,000km3/a available the abstracted 4,000 appear small. One should, however, not forget that these figures are averaged in time and space and therefore hide the real problem, e.g. droughts and floods. One can still use the ratio a of withdrawals and available renewable resources as an indicator. Due to the variability of the quantities involved, it is the experience that a value of a>0.4 already reflects severe scarcity. On a global scale a=0.31 is found (Alcamo et al., 2003). This indicates that scarcity on a global level is a reality today, with the arid world already experiencing very severe scarcity problems.

Water resources of arid areas

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2 SUSTAINABILITY Sustainable water management is a practice, which avoids irreversible or quasiirreversible damage to the resource water and other natural resources linked to it, such as soil and ecosystems. Such a practice conserves the ability of the resource water to provide its services including ecological services. Water scarcity and poverty are often the causes of non-sustainable behavior as they lead to overexploitation and depletion of stocks. What are the relevant issues for global sustainability in the water sector? To identify big and possibly existential problems for whole regions we have to look for ubiquitous negative global trends. In that sense there are a number of non-sustainable practices, which are of global importance. Above all, these are – the overpumping of aquifers, – the destruction of wetlands, – the salination of soils, and – the pollution of aquifers with persistent pollutants. Globally about 800km3/a of freshwater are abstracted from aquifers. About one quarter of this abstraction is non-sustainable in the sense that it is not replaced by recharge, i.e. it is taken out of the available stock. On the Arabian Peninsula, in North Africa, China and the arid Western United States for example, abstractions for large-scale irrigation have withdrawn large quantities of fossil water, which under present climatic conditions are not replenished any more. The global area of wetlands has diminished by 50% since the year 1900. This has a dramatic impact on species diversity. It is a consequence of the competition between natural and man-made ecosystems for land and water resources. The tendency is unbroken. Of the 260 million ha of irrigated farmland in the world about 80 million are affected by soil salination. Salination is a common phenomenon in hot climates. It occurs if in a soil more salt is deposited by evapotranspiration than is removed by drainage. In irrigated agriculture, the most common mechanism leading to salination is the groundwater table rise due to seepage of irrigation water. Once a groundwater table is closer than 2m to ground level, capillary rise leads to direct evaporation from groundwater and to fast salination of the topsoil. Finally, there is the deterioration of groundwater quality by persistent pollutants. One might expect that among those chlorinated hydrocarbons are the most important. This is only true for industrialized countries while globally the most prominent pollutant is salt, especially in arid regions and coastal areas, where seawater intrusion occurs. In principle, all these violations of sustainability are reversible. But the required timescales are on the order of several generations. For all practical purposes these damages are irreversible. In the following, three examples from projects of the Institute of Hydromechanics and Water Resources Management are shown, illustrating the first three globally important sustainability problems. The common features of these examples are that – there is water scarcity (all three areas are in arid or semi-arid climate zones), – a model is developed to analyze and understand the system,

Sustainable water management in arid and semi-arid environments

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– the model is used for the testing of management strategies and/or for optimization, and finally – the connection is made to the field of socio-economics.

3 OVERPUMPING OF THE NORTH-WEST SAHARA AQUIFER SYSTEM The North Western Sahara is underlain by one of the world’s largest aquifer systems, which covers approximately 1,000,000km2 and consists of two major aquifers, the deeper Continental Intercalaire (CI) and the shallower Complexe Terminal (CT) (Fig. 1). Their water resources are being utilized by the three countries Algeria, Tunisia and Libya mainly for irrigation purposes. The system nowadays hardly receives any recharge. At most 30m3/s are estimated as recharge

Figure 1. Overview of the NorthWestern Sahara aquifer system and its water balance. along the southern flank of the Saharan Atlas where the aquifers strike out (ERESS, 1972). Compared to the size of the system, this recharge flux is—if at all—only of importance locally. The system discharges mainly via the sink of the Chotts or salt lakes, which are the topographic lows of the endorrheic basin. Here approximately 10m3/s evaporate. A very small portion of no more than 5m3/s is thought to discharge to the sea in Libya. Until 1950 abstractions were small. Since then the population has tripled and with it the amount of water pumped for irrigation. An estimated rate of 180m3/s is abstracted today. As a consequence the large springs in the vicinity of the Chotts have run dry (Fig. 2). Artesianism has vanished over large areas and the water, which before flowed at no energy cost, now has to be pumped.


6

The present situation is characterized by an abstraction, which is 6 times as large as the recharge rate. This brings up the question whether a non-renewable resource should be used at all. Looking at the size of the system and its storage coefficient, an enormous amount of about 100000km3 of water is stored. About one tenth of that amount can be accessed with an economically feasible drawdown of less than 250m. With a projected future withdrawal rate of 500m3/s the total resource can still last for about 600 years. But this water comes at a price. First, energy is necessary for its pumping and distribution and investments in pipes and boreholes have to be made. Second, pumping can lead to deterioration of water quality. Sources of pollution are various. Near the Chotts for example, large drawdowns will reverse the hydraulic gradient, which under natural conditions is always directed from the oases to the Chotts. A reversed gradient mobilizes brine, which finally leads to degradation of the water quality pumped and contributes to the die-off of oases. A similar phenomenon is observed along the coast, where overpumping leads

Figure 2. Development of discharges from springs in Southern Tunisia (1887–1985) (Source: Mamou, 1990)


Figure 3. Modeled head distribution in CI, 1950 (heads from 530 mamsl to 70 in steps of 35m).

Figure 4. Predicted head distribution in CI, 2050 for planned pumping (heads from 530 mamsl to –250 mamsl in steps of 55m).

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8

to seawater intrusion. Salt water can also be mobilized from lower saline aquifers such as the Turonian. With a reduced pressure overburden this confined aquifer can infiltrate at a larger rate into the CT from below. A numerical model of the system has been built which demonstrates that with the required total pumping rate by 2050 large areas of the presently strongly pumped regions will face a piezometric decline with economically infeasible drawdowns of more than 250m below ground level (area with sawtooth pattern in Fig. 4). At the same time the constraints for water quality locally can no longer be fulfilled. The groundwater model was then coupled with optimization algorithms to find allocation patterns that conform to demand, drawdown and quality constraints in time while minimizing overall provision costs. The wells in an optimal scheme spread out over the area to equilibrate distribution cost with pumping cost, which depend on drawdown. They further spread to the CI from the CT. Two variants were analyzed. In the first, the existing pumping locations were used and the pumping rates at those constituted the set of decision variables. At the Chott cells, gradient constraints were introduced to prevent gradient reversal and thus preserve the productivity of the oases. On the whole the costs are exploding over time, with the running cost of water increasing by a factor of about 30 in 50 years (Siegfried, 2003). In a second variant, pumping at any location was allowed with the costs being the only criterion for choosing a specific cell. The results show that compared to the first variant much better abstraction schemes are possible with considerably lower running cost (and total costs) over the next 50 years. However interesting such a scenario is, it would require a complete renewal of infrastructure. Realistically, only a gradual transition from today’s pumping well distribution to a more favorable one in the future will be feasible. The model demonstrates that it is possible to minimize pumping cost to reasonable levels and provide water for the next 50 years. This time however must be used to develop alternatives. All optimization runs were carried out ignoring national borders in order to assess benefits from cooperative management. As the results demonstrate, cooperation between the three countries involved brings considerable advantage in the exploitation of the resource. Nevertheless, in the long run the conservation of the oasis culture requires heavy subsidies as the substitution between the production factors water and capital progresses. 4 MANAGEMENT OF THE OKAVANGO DELTA, BOTSWANA The Okavango River flows from the Benguela plateau of Southern Angola in southeastern direction through the northern tip of Namibia and then into Botswana, where it forms an inland


9

Figure 5. Satellite image of the Okavango Delta (length from right to left about 550km). Delta in which it is consumed completely by evapotranspiration (Fig. 5). The Delta is one of the largest wildlife areas in Africa and is an attraction for numerous tourists. The yearly floods of the river turn a large area of the Delta into a seasonal swamp (Hutchins et al., 1976; Scholz et al., 1976; McCarthy et al., 1986; Thomas and Shaw, 1991; Ellery et al., 1993; McCarthy et al., 1993; McCarthy and Ellery, 1994; Modisi et al., 2000; Gumbricht et al., 2001). As the flood takes 3 months to propagate from the inflow at Mohembo to the distal side at Maun, it is out of phase with the local rainy season and thus increases the water availability over the year. The upstream countries are discussing plans to abstract water from the river and/or build dams for electricity production or agricultural purposes. In Botswana itself, various sectors of the economy have also proposed to make use of the Okavango water, be it for agriculture or for mining purposes. All measures proposed threaten the existence of the Delta as the unique ecosystems it is. Both abstraction of water in the upstream and acceleration of the through-flow by dredging of channels etc. will cause a decrease in the size of the seasonal swamp. In order to assess the impact of hydraulic measures on the size and distribution of the flooded area a numerical model was constructed which contains the surface water and the groundwater in two coupled layers. In an innovative approach satellite data on the time-varying size of the Delta were used to calibrate the model (McCarthy et al., 2003; Bauer et al., 2004). Further data used in this approach are a high-resolution digital terrain model obtained from the flooding patterns and the related vegetation patterns (Gumbricht et al., 2001, 2003), the inflow at Mohembo, the precipitation from METEOSAT data (Herman et al., 1997), the


10

evapotranspiration from multi-spectral satellite data (Bastiaanssen et al., 1998a, 1998b), and last not least local measurements which are routinely performed by the Botswana Department of Water Affairs. The model is able to reproduce satisfactorily the seasonal dynamics of the flooded areas both in total extent and in distribution over a period of 20 years for which data are available (Fig. 6). The sink of all water is essentially the evapotranspiration by the plant cover. This process also governs the distribution of salts in the Delta. Pronounced salt crusts indicate areas, which are natural disposal sites of salts. Their continued functioning is of considerable importance to the conservation of the Delta. This process will be incorporated in a future version of the model. One example of measures with potentially serious impacts on the Delta is the abstraction of water upstream of the inflow (Fig. 7). It is seen that an abstraction is amplified i.e. the relative reduction in area is considerably larger than the relative reduction in inflow. Dams have an effect on both inflow reduction and temporal inflow distribution. Model calculations showed that the change in input distribution not necessarily is detrimental to the size of the flooded area. A more stretched out flood will bring water further downstream. Morphological changes such as dredging of channels and removal of blockages by papyrus have also a pronounced effect, not so much on the total flooded area as on the distribution of flooded areas within the Delta (Bauer et al., 2004).

Figure 6. Observed and modeled flooding frequency (%).


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Figure 7. Flooded area for different abstraction scenarios in comparison with the modeled development of the last 20 years. The local abstraction for household consumption, be it directly or from the aquifer, is so small that it will at no stage be of relevance for the Delta. The tentative ranking of different interventions according to their severity is as follows: – abstractions larger than 2m3/s in the upstream, – building of large dams in the upstream, – change to a drier climate, – morphological changes (dredging, cutting of vegetation, tectonics), – local drinking water supply. The model can provide a quantitative basis for the political debate between the three riparian nations. It is clear that the conservation of the Delta must bring some revenue to the upstream in exchange for the guaranteed inflow. The key parameter for an administrable negotiated solution will be the minimum inflow at Mohembo and its seasonal variability. 5 SALINATION OF SOILS AND WATER IN YANQI BASIN, XINJIANG, CHINA The third example studies a region in China’s arid west. The Yanqi basin is formed by the lowlands of the Kaidu River and Lake Bostan (Fig. 8). The area has been used intensively for agriculture over the past 50 years. The main products are grapes, cotton and red peppers.


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Figure 8. Satellite map of the Yanqi basin showing the irrigation areas along the Kaidu River, Lake Bostan and the Kongque River. As precipitation is only 70mm/a and thus negligible compared to the potential evaporation of 1800mm/a, no agriculture is possible without irrigation. The last 50 years have seen a tremendous growth of the population. This has led to a strong increase in agricultural production. The intensive irrigation with river water caused a water table rise, followed by serious soil salination. To maintain production, over-irrigation is required to push salt from the surface beneath the root zone. This practice increases the amount of water used per unit crop and contributes again to water table rise. A vicious circle is triggered, leading to higher and higher salinity in the water flowing off the irrigation area both in the subsurface and in the drains. One could argue that the applied irrigation techniques and efficiencies in the Yanqi Basin are sustainable, as a steady state has been reached (the amount of salt transported out of the Yanqi Basin is equal to the amount of salt imported by the Kaidu) and production stabilized on a level still profitable. This of course cannot be called sustainable because only the needs of the farmers in this particular irrigation system are satisfied. With the rising groundwater table and the increased non-productive evaporation of water the salinity in the lake has increased and the lake level has fallen. The amount of water available for the downstream of lake Bostan, carried by the Kongque River, has decreased thus limiting natural vegetation growth and agriculture in the so called Green Corridor. The Green Corridor is a landscape, which extends down to Lop Nor and is characterized by the riverine desert poplar forests. Today, no water reaches Lop Nor due to the high consumptive use in the upstream irrigation systems. In order to improve the situation of the system as a whole, a number of measures in the upstream have been proposed (Dong, 2001). They include


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– the reduction of irrigation area, – substitution of irrigation water from the river by groundwater thus guaranteeing that the groundwater table stays below critical levels, – changes in the crop mix and irrigation techniques (e.g. drip irrigation for grapes), – the transfer of water directly from Kaidu river to the Kongque river bypassing the lake, – the lowering of the lake level in order to reduce non-productive evaporation of the lake and others. In an integrated modeling approach all these options will be investigated. Again, some relevant data can be obtained using remote sensing techniques. In this case we constructed a digital terrain model from stereo images of radar satellites based on methods described by Zebker and Goldstein, 1986. The absolute elevations were obtained from single point DGPS measurements (Fig. 9). The ground surface elevation is of particular interest in salination problems as evaporation from groundwater is a function of the distance to groundwater table. Hence salinity observed at the

Figure 9. Digital terrain model of the Yanqi basin.


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Figure 10. Correlation between measurements at ground control points (GCP) of soil conductivity and spectral match to salt pixel. ground level is a data type, which allows the regional verification of the groundwater model. The distribution of surface salinity was obtained from multispectral ASTER data and measurements in the field. Based on the spectral response of a completely salinized pixel, the closeness of any pixel to this reference is determined yielding an uncalibrated salinity map. To convert these values into salinity or its physical measure of electrical conductivity, a calibration with ground truth is required. The ground truth was obtained both by single core samples and less time-consuming geophysical measurements. A good correlation between ground truth and the uncalibrated salinity map was found (Fig. 10). Of course, this correlation only holds for the non-irrigated areas. The salinity map (Fig. 11) clearly shows the salt accumulation in the paths between fields while in the irrigated fields themselves no increased salinity is visible due to overirrigation. While a coupled groundwater-surface water model is still under development, preliminary estimates are already available on the basis of a multi-box approach with the irrigation area, the aquifer and the lake being the respective boxes. Despite the fact that the box approach is a major simplification, it demonstrates that steady states for groundwater tables as well as salt concentration exist. Depending on how water in a steady state is exported from the system, reaching a steady state salt concentration can take a very long time compared to reaching a steady state in groundwater tables (Fig. 12). The steady state salt concentration is directly determined by


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Figure 11. Salinity map obtained from a multispectral satellite image.

Figure 12. Steady state for groundwater tables (hss, m below surface) and salinity (css, g/l) in the Yanqi basin aquifer as functions of applied irrigation water (in 107m3/a). the ratio of the flux of water draining from the aquifer into the lake and the groundwater recharge. Furthermore, the box approach shows that the rate of accumulation of salt increases rapidly as soon as direct evaporation from the aquifer occurs. Pumping groundwater for irrigation purposes would not only reduce the need for overirrigation, but also directly contribute to the water availability downstream. This solution is more expensive as groundwater comes at about 10 times the price of surface water. However, if the water table can be kept low by pumping groundwater, the conservation of soil and the increased availability of surface water in the downstream might strike the balance with a higher price of water.


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6 CONCLUSIONS In arid countries the problems of sustainability in the water sector are prominent. On a worldwide basis the three subjects discussed are the most widespread. They show several common features. Water management in the arid and semi-arid environment must include salt management. Modern tools such as remote sensing, geophysics and modeling hydrological science help even in regions with weak infrastructure to quantify the implications of human interaction and to give advice to decision makers on the sustainability of water management practices. Models summarize the state of affairs and are the only means to make predictions. They are bound to be crude and simulations will always be idealized. Still, they can serve as points of reference. A further common feature is that sustainable solutions require the system boundary to be taken sufficiently large, often transgressing political boundaries. While science can give some decision support, the decisions for or against sustainability are made in the political arena. REFERENCES Alcamo, J., Doll, P., Henrichs, T., Kaspar, F., Lehner, B., Rosch, T. & Siebert, S. 2003. Development and testing of the WaterGAP 2 global model of water use and availability. Hydrological Sciences Journal-Journal Des Sciences Hydrologiques, 48(3):317–337. Bastiaanssen, W.G.M., Menenti, M., Feddes, R.A. & Holtslag, A.A.M. 1998a. A remote sensing surface energy balance algorithm for land (SEBAL). 1. Formulation. Jnl. of Hydrology, 212– 213:198–212. Bastiaanssen, W.G.M., Pelgrum, H., Wang, J., Ma, Y., Moreno, J.F., Roerink, G.J. & van der Wal, T. 1998b. A remote sensing surface energy balance algorithm for land (SEBAL). 2. Validation. Jnl. of Hydrology, 212–213:213–229. Bauer, P., Gumbricht, T. & Kinzelbach, W. 2004. A large-scale coupled surface water/ground water model of the Okavango Delta, Botswana. Water Resources Research, submitted. Dong, X., Jiang, T. & Jiang, H. 2001. Study on the pattern of water resources utlilsation and environmental conservation of Yanqi Basin. In: G.Li (Ed.), Development, Planning and Management of Surface and Groundwater Resources. IAHR congress proceedings. Tsinghua University Press, Beijing, China: 333–340. Ellery, W.N., Ellery, K., Rogers, K.H., McCarthy, T.S. & Walker, B.H. 1993. Vegetation, hydrology and sedimentation processes as determinants of channel form and dynamics in northeastern Okavango Delta, Botswana. African Jnl of Ecology, 31:10–25. ERESS 1972. Etude des Ressources en Eau du Sahara Septentrional. Rapport sur les Résultats du Projet, Conclusions et Recomm endations, UNESCO, Paris. Gumbricht, T., McCarthy, T.S. & Bauer, P. 2003. Microtopography of the Okavango Delta using correlation between land cover and elevation. Earth Surface Processes and Landforms, in press. Gumbricht, T., McCarthy, T.S. & Merry, C.L. 2001. The topography of the Okavango Delta, Botswana, and its tectonic and sedimentological implications. South African Jnl. of Geology, 104:243–264. Herman, A., Kumar, V.B., Arkin, P.A. & Kousky, J.V. 1997. Objectively Determined 10 Day African Rainfall Estimates Created for Famine Early Earning Systems. International Journal of Remote Sensing, 18(10):2147–2159. Hutchins, D.G., Hutton, L.G., Hutton, S.M., Jones, C.R. & Loenhert, E.P. 1976. A summary of the geology, seismicity, geomorphology and hydrogeology of the Okavango Delta, Geological Survey Botswana, Gaborone.


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Mamou, A. 1990. Charactéristiques et evaluation des resources en eau du sud Tunisien. Dissertation, Université de Paris-Sud, Centre d’Orsay. McCarthy, J., Gumbricht, T., McCarthy, T.S., Frost, P.E., Wessels, K. & Seidel, F. 2003. Flooding Patterns of the Okavango Wetland in Botswana between 1972 and 2000. Ambio, 32(7):453–457. McCarthy, T.S. and Ellery, W.N. 1994. The effect of vegetation on soil and ground water chemistry and hydrology of islands in the seasonal swamps of the Okavango fan, Botswana. Journal of Hydrology, 154: 169–193. McCarthy, T.S., Ellery, W.N., Rogers, K.H., Cairncross, B. & Ellery, K. 1986. The roles of sedimentation and plant growth in changing flow patterns in the Okavango Delta. South African Journal of Science, 82: 579–584. McCarthy, T.S., Green, R.W. & Franey, N.J. 1993. The influence of neo-tectonics on water dispersal in the north-eastern regions of the Okavango swamps, Botswana. Journal of African Earth Sciences, 17(1): 23–32. Modisi, M.P., Atekwana, E.A., Kampunzu, A.B. & Ngwisanyi, T.H. 2000. Rift kinematics during the incipient stages of continental extension: Evidence from the nascent Okavango rift basin, northwest Botswana. Geology, 28(10):939–942. Postel, S.L., Daily, G.C. & Ehrlich, P.R. 1996. Human appropriation of renewable fresh water. Science, 271(5250):785–788. Scholz, C.H., Koczynski, T.A. & Hutchins, D.G. 1976. Evidence of incipient rifting in Southern Africa. Geophysical Journal of the Royal Astronomical Society, 44:135–144. Siegfried T. 2003. Management of internationally shared groundwater resources in semiarid and arid region s: the Northern African Aquifer System. In E.Servat et al. (eds), Hydrology of Mediterranean and Semiarid Regions, IAHS Publ. No. 278, 2003. Thomas, D.S.G. & Shaw, P.A. 1991. The Kalahari Environment. Cambridge University Press, Cambridge. Zebker, H.A. & Goldstein, R.M. 1986. Topographic Mapping from Interferometric Synthetic Aperture Radar Observations. Journal of Geophysical Research-Solid Earth and Planets, 91(B5):4993–4999.

Theme A: Problems in obtaining hydrological and geohydrological data

Slug tests in fractured rock formations: value, pitfalls and misinterpretations P.D.Vermeulen & G.J.van Tonder Institute for Groundwater Studies, University of the Free State, Bloemfontein Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: Currently slug tests in South Africa are used with two objectives in mind: (i) to get a first estimate of the yield of a borehole (relationship obtained by Viviers et al., (1995) and (ii) to estimate the Kvalue (or T-value) of the aquifer in the vicinity of the borehole. The paper shows that the use of currently available slug test interpretation methods to analyse slug tests in fractured rock aquifers to estimate a T or K-value is problematic. The estimated value is dependent on the flow thickness (thickness of the part of the aquifer in which flow occurs due to the slug input). If this thickness of flow is known, the estimated K-value is more representative of that of the fracture zone. By using the total thickness of the formation for the estimation of the K-value in slug test analysis, the estimated K-value (and thus KD-value) does not represent the T-value of the formation.

1 INTRODUCTION In performing a slug test, the static water level in a borehole is suddenly lowered or raised. This is usually done by lowering a closed cylinder into a borehole. The cylinder replaces its own volume of water within the borehole, thus increasing the pressure in the borehole. As the equilibrium in the water level is changed, it will recover or stabilise to its initial level. If the rate of recovery or recession of the water level is measured, the transmissivity or hydraulic conductivity of the borehole can be determined (Kruseman and De Ridder, 1994). In South Africa slug tests are conducted for the following two reasons: ● To estimate the hydraulic conductivity (K) of the aquifer in the vicinity of the borehole and ● To get a first estimate of the yield of a borehole (Vivier et al., 1995).


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Vivier et al. (1995) performed slug tests on 32 boreholes, of which the maximum yield was known and they then derived empirically the following formula (there is a 93% correlation between the actual yield and the yield estimated with the formula): Q=117155.08t−0.83 (1) where: Q=yield of the borehole in l/h and t=recession time of the slug test in seconds (90% recovery). Usually the Cooper method (Cooper et al., 1967) or the Bouwer and Rice method (1976) is used to estimate the K-value (or T-value in the case of the Cooper method). In the following section slug test results, as well as pumping and tracer test results for borehole UO5 on the well-known Campus Site of the University of the Free State, South Africa (Figure 1) will be discussed to illustrate the problems associated with the interpretation of slug tests in a borehole drilled in a fractured aquifer.

Figure 1. Map of the RSA.

Slug tests in fractured rock formations

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Figure 2. Diagram of the geological formation at the Campus Test Site (relative thickness of the aquifers in brackets). 2 BOREHOLE UO5 ON THE CAMPUS SITE The Campus Test Site is underlain by a series of mudstones and sandstones from the Adelaide Subgroup of the Beaufort Group of formations in the Karoo Supergroup (Figure 2). There are three aquifers present on the Site. The first, a phreatic aquifer, occurs within the upper mudstone layers on the Site. This aquifer is separated from the second and main aquifer, which occurs in a sandstone layer of between 8 and 10m thick, by a layer of carbonaceous shale with a thickness of 0.5 to 4m. The third aquifer occurs in the mudstone layers (more than 100m thick) that underlie the sandstone unit.


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Figure 3. Acoustic scan of borehole UO5 at a depth of 20m to 25m below the surface.


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Figure 4. Borehole video image of the fracture zone in borehole UO5 showing a fracture-zone thickness of about 200mm.

Figure 5. Constant rate pumping test data of UO5. Table 1. Hydraulic parameters estimated for UO5.


Parameter

26

Value

T of formation* (m2/d) 19 K of fracture zone (m/d) 3600 T of fracture zone (m2/d) 576 K of matrix (m/d) 0.17 T of matrix** (m2/d) 3 *Average for fracture+matrix, obtained from Cooper-Jacob fit to late drawdown values. **For 20m thickness.

A major characteristic of the main aquifer is the presence of a horizontal fracture that coincides approximately with the centre plane of the sandstone layer, and which intersects all 11 boreholes with significant yields on the Site, of which UO5 is one. The remaining 14 boreholes all have very insignificant yields. The fracture zone thickness is approximately 10mm, but the adjacent 200mm of sandstone is also highly permeable. Figure 5 shows a graph of the data from a constant rate test conducted on UO5 at a rate of 1.25L/s. Measurements were also taken in the observation borehole UO6. These pumping test data were analysed with a numerical 3D model (Van Tonder et al., 2001), and the following parameters were estimated in Table 1. The thickness of fracture zone (referred to in Table 1) was obtained from tracer tests and the borehole video, and is 0.16m. The hydraulic parameters given in Table 1 are regarded to be accurate (Van Tonder et al., 2001). It would now be interesting to analyse the data of a slug test (Figure 6) conducted on borehole UO5 and compare the estimated values with the values given in Table 1. The 90% recovery occurred after about 9 seconds, and using Equation (1) the yield of borehole UO5 is estimated as 5.3L/s. The tested blow yield of borehole UO5 was 6L/s during drilling. The Bouwer and Rice method (1976) was applied to the data in Figure 6. The Bouwer and Rice equation reads: (2) where: rc=radius of the unscreened part of the borehole where the head is rising rw=horizontal distance from the borehole centre to the undisturbed aquifer Re=Radial distance over which the difference in head h0 is dissipated in the flow system of the aquifer


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Figure 6. Data collected during a slug test conducted on UO5. Table 2. Estimated K-values with the Bouwer and Rice method (1976) for different values of the flow thickness. Thickness open to flow (m)

K (m/d)

30 20 10 1 0.16 0.001

12 17 32 231 541 3600

T (m2/d) 360 340 320 231 86 3.6

d=length of the borehole screen or open section of the borehole h0=head in the borehole at time=0 ht=head in the borehole at time t The estimated K-value of Bouwer and Rice is dependent on the thickness open to flow, d, and Table 2 shows the different K-value estimates for different flow thicknesses. Note that a flow thickness of 30m will indicate the depth from the water level to the end of the borehole and that a thickness of 0.16m is the thickness of the fracture zone in borehole UO5. 3 DISCUSSION Comparison of Table 1 and Table 2 shows the following important issues: ● An incorrect K-value is obtained from the slug test if the thickness of the aquifer (total formation) is used as the flow thickness. For a thickness of 30m, a K-value of 12m/d


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(or T=360m2/d) is estimated from the slug test, which is neither the T-value of the fracture zone nor the T-value of the matrix. ● For a flow thickness of 0.16m (i.e. the thickness of the fracture zone), a K-value of 541m/d is estimated with the Bouwer and Rice (1976) slug test method. This estimated K-value is more representative of the K-value of the fracture zone. ● The average T-value of the formation, which is important for management purposes, was estimated as 19m2/d from the constant rate pump test. It is impossible to estimate the T- or K-value of the aquifer formation via a slug test.

4 CONCLUSIONS The use of the current available slug test interpretation methods to analyse a slug test in a fractured rock aquifer to estimate a T- or K-value is problematic. The estimated value is dependent on the flow thickness (thickness of the part of the aquifer in which flow occurs due to the slug input). If this thickness of flow is known, the estimated K-value is more representative of that of the fracture zone. By using the total thickness of the formation for the estimation of the K-value in slug test analysis, the estimated K-value (and thus KD-value) does not represent the T-value of the formation. REFERENCES Bouwer, H. & Rice, R.C. 1976. A slug test for determining hydraulic conductivity of unconfined aquifers with completely pr partially penetrating wells. Water Resources Research, 12:423–428. Cooper, H.H, Bredehoeft, J.D., & D Papadopulos, I.S. 1967. Response of a finite-diameter well to an instantaneous charge of water. Water Resources Research, 3:263–269. Kruseman, G.P. & de Ridder, N.A. 1994. Analysis and Evaluation of Pumping Test Data. 2nd ed. International Institute for Land Reclamation and Improvement. Publication 47. Wageningen, the Netherlands: 237–247. Vivier, J.J.P., Van Tonder, G.J. & Botha, J.F. 1995. The use of slug tests to predict borehole yields: correlation between the recession time of slug tests and borehole yields. In Conference Proceedings: Groundwater’95: Groundwater Recharge and Rural Water Supply, Midrand, South Africa. Van Tonder, G.J., Botha, J.F., Chiang, W.H., Kunstmann, H. & Xu, Y. 2001. Estimation of the sustainable yields of boreholes in fractured rock formations, Special issue of Journal of Hydrology: No 241.

Flow simulation model performance assessment using entropy approach A.M.Ilunga Civil Engineering, University of the Witwatersand, South Africa D.Stephenson Civil Engineering, University of Botswana, Gaberone, Botswana Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: Hydrological data (e.g. rainfall, river flow, etc) are used in water resources planning and management for planning reservoir and operation. However, it happens sometime that the appropriate site where a hydraulic structure (e.g. reservoir) should be built has no available data due for example to inaccessibility to erect a flow gauging station, etc. This is particularly a problem in arid areas. Very often hydrologists make use of simulation models to estimate the flows data series at the very site from the nearby stations and using some physical characteristics of the catchment area. In this paper, a merely methodology is proposed to evaluate the performance of simulation models in terms of entropy (e.g. reduction of the uncertainty of flows) before and after applying a model to the site. This reduction should be above a certain threshold value for the model to be retained as performing well. An example is illustrated through RAFLER model, which is used to simulate yearly flows at Braamhoek.

1 INTRODUCTION For planning, management and effective control of water resources systems, a considerable amount of data on hydrologic variables such as rainfall, streamflow, etc. are required. It sometime happens that the appropriate site where a reservoir should be built has no available data due for example to inaccessibility to erect a flow gauging station. This is particularly a problem in arid areas. Physical models, semi-distributed models, statistical models, conceptual model, embracing probabilistic, fitting curve, black box, etc are often used to simulate/estimate flows. In this paper, a merely methodology is proposed to evaluate the performance of simulation models in terms of entropy (e.g. reduction of the uncertainty of flows) before and after applying a model to the site in a similar way of Panu (1992). These authors used entropy approach for infilling hydrological data problems (e.g. reduction of uncertainty before and after infilling the


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data series), while in this paper the same approach is applied to cases where no data series is available at all at the target site. In very recent paper (see, Ilunga and Stephenson, 2003b) the methodology for evaluating the model performance was roughly used but it was not explained systematically as done in this paper. It should be noted that the reduction evoked above should be above a certain threshold value for the model at hand to be retained as performing well. An example is illustrated through RAFLER model, which is used to simulate yearly flows at Braamhoek. 2 INFORMATION CONTENT OF HYDROLOGICAL VARIABLES Traditionally, the information content of a hydrological variable can be measured through variance, which shows the variability of the hydrological variable with respect to its mean. However this approach was criticized for cases where information available about the hydrological variable is little (Singh, 1998). Since 70’s hydrologists tried to find another way of measuring information by theoretic entropy (a term borrowed from communication, see Shannon & Weaver, 1949). Thus the concept has been applied in water resources (Singh & Florentino, 1992; Amorocho & Espildora, 1973) and water related fields. The entropy is considered as a measure of the amount of chaos or lack of information about a system. The entropy can be viewed as a measure of ignorance about the system described in classical sense by a probability distribution. Indirectly, it measures the information about the system. Mathematically entropy of a system {xi} is defined in its discrete form by the following expression (1) where K: is a function of the base used or the scale factor (bits for base 2, napiers for base e, decibels for base 10), i=1, 2,…, n and pi is the probability of occurrence of the event i. It can be shown that the value of H(X) reaches its maximum when all variate values xi are equally likely, that is, when the outcome has maximum uncertainty (Amorocho & Espildora, 1973). In this case the entropy becomes Hmax (X)=log n (2) The theoretic entropy definition was extended to hydrology. Hence entropy is considered as a measure of the degree of uncertainty of random variable hydrologic processes (Amorocho & Espildora, 1973). Since the reduction of the uncertainty by means of making observations is equal to the amount of information gained, the entropy criterion indirectly measures the information content of a given series of data (Harmancioglu et al., 1994). It arises that the distribution of the variable can be unknown a prior although some of its properties may be known, e.g. mean, variance, normality condition. These proprieties (information) enable to determine the distribution of the variable, which maximizes the entropy function. In this way the distribution is consistent with the available information,

Flow simulation model performance assessment using entropy approach

31

but retains maximum uncertainty within the feasible domain and thus ensures the least bias; that is the principle of maximum entropy (POME) introduced by Jaynes in 1968. This principle has been applied intensively in hydrology in the last two decades. 3 ENTROPY APPROACH AS HYDROLOGICAL MODEL PERFORMANCE EVALUATION Amorocho and Espildora (1973) suggested that the mutual information (between the observed values and the simulated ones) could be used as a criterion in the selection of hydrological models; e.g. rainfall-runoff prediction. Note that the mutual information concept is derived from entropy notion and for more details; the reader is referred for example to the above-mentioned paper. Later the directional information transfer index (DIT) appeared as a generalization of the mutual information Yang and Burn (1994) and was used for dependency evaluation between streamflow gauging station pairs. Recently, it is argued that since mutual information is used for model performance assessment, its generalization i.e. DIT can be extended to model performance evaluation (Ilunga & Stephenson, 2003a). The above considerations are valid when the estimated values have to be compared to the observed ones. In that respect statistical criteria such as root mean square error, etc can be also used to crosscheck the results (Ilunga and Stephenson, 2003a). However it becomes difficult to use these considerations when missing values are encountered in the data series. Thus Panu (1992) introduced the notion of reduction of uncertainty of the hydrological variable before and after infilling the data series. The reduction of uncertainty Re d(%) at a given site as defined by Panu (1992) can be given as follows: (3) where Hcc and Hcomp are entropy values before and after infilling the data series respectively. It should be noted that this concept was applied to cases of consecutive missing data values, e.g. hydrological data exist before and after the missing values. 4 PROPOSED METHODOLOGY Panu (1992) used expression (3) for infilling data problems, in other words some data exist before infilling process. In this paper the same expression (3) is proposed for cases where no available flow data exist at all at the site. It is more natural to say that a case where no data is available, the uncertainty is higher than a case where data exist. Thus it is assumed that the uncertainty should be maximum (e.g. if all hydrological events would occur equally likely) at a site where no data is known. Thus, in this case expression (3) can be re-written as (Ilunga & Stephenson, 2003b): (4)


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Where Hmax is defined by expression (2) The following are the different steps for evaluating the performance of a flow simulation model for cases where no data exist at all at given site. 1. Having the physical parameters of the catchment area and information (e.g. rainfall) from the nearby sites, compute the simulated flows. 2. Compute the frequency (probability) distribution of the flows. 3. Compute the marginal entropy of the site using formula (1) and set the entropy before simulating flows to its possible maximum value, e.g. see formula (2). 4. Compute the reduction of entropy at the site using expression (4) and set a threshold reduction of entropy to an arbitrary value. If the computed value for the reduction is greater or equal than the threshold value, the model is considered as performing well. Otherwise, the model performs poorly. Terminate.

5 SHORT NOTE ON RAFLER RAFLER is an acronym for Rainfall Flow Erosion. A model (RAFLER) is a deterministic model based on the physics of runoff, soil infiltration and soil transport and which converts rainfall data to runoff over a length of time, e.g. years. The model uses monthly rainfall figures to reproduce monthly stream flow series and soil erosion. Some simplification is made to enable the model to be run with a minimum of data. And the rainfall period each month is estimated from the number of rain days to enable true flow rates to be calculated. This model requires a number of modules including catchment, channels and reservoirs. The general theoretical background of the model can be traced in Stephenson (2002). 6 STUDY AREA AND DATA AVAILABILITY Braamhoek is situated in the Free State, in South Africa. The catchment area is about 62km2. Neither rainfall data nor stream flow data is available at this particular site. Thus it was possible to simulate flows at Braamhoek using rainfall data from the nearby sites; viz at Van Reenen (MAP=1002mm/month); at Moorside (MAP=839mm/month) and at Baldergow


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Figure 1. Simulated yearly frequency (probability) distribution at Braamhoek. Table 1. Model performance evaluation at Braamhoek.

Before applying RAFLER Applying RAFLER

Marginal entropy (Napiers) at Braamhoek

Reduction of uncertainty (%) at Braamhoek

4.47

−

1.65

63.06

(MAP=887mm/month). The monthly rainfall data (1916–2002) were obtained from the Weather Bureau, South Africa. 6.1 Application of the methodology to Braamhoek The application of the model, i.e. RAFLER to simulate the total annual flows (from 1916–2002, e.g. 87 data points) at Braamhoek site gave the following results. Figure 1 from which the entropy calculations were possible shows the probability (frequency) distribution estimated from the model. The threshold value of the reduction of uncertainty was set to a value of 50% napiers. Table 1 shows the results of entropy calculations before and after applying RAFLER models. It is therefore concluded that the reduction in uncertainty of the yearly flows at


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Braamhoek was 66.06% by this model. This value is the equivalent of information inferred about the site using RAFLER model. This model could be thought to perform well. Thus RAFLER model could be used for flow prediction at Braamhoek with regard to the total yearly flows. Nonetheless the model needs to be tested on other flow regimes for that specific site. 7 CONCLUSION The focus of this paper was to give a methodology for evaluating the performance of simulation models using entropy approach. The methodology has been tested with RAFLER model on Braamhoek site where records were simulated. Recall that this methodology was roughly used in Ilunga and Stephenson (2003a), but without presenting systematically the steps involved as been done in this paper. The computations from the entropy criterion showed that RAFLER model could be used for simulating the total yearly flows at Braamhoek when a threshold value of 50% is considered for the reduction of uncertainty before and after simulation. Investigation should also be done on other flow regimes. REFERENCES Amorocho, J. & Espildora, B. 1973. Entropy in the assessment of uncertainty in hydrologic systems and models. Water Resources Research, 9(6):1511–1522. Harmancioglu, N.B., Alpaslan & Singh, V.P. 1994. Assessment of the entropy principle as applied to, water quality monitoring network design. Stochastic and Statistical Methods in Hydrology and Environmental Engineering., 3:135–148. Ilunga, M. & Stephenson, D. 2003a. Performance of hydrological data infilling techniques using entropy approach: Expectation maximization algorithms. 11th South African National Hydrology Symposium, Port Elizabeth, South Africa: 6. Ilunga, M. & Stephenson, D. 2003b. Entropic measures for comparing flow simulation models at Bedford site. Paper submitted to the J. Hydrology, Elsevier. Panu, U.S. 1992. Application of some entropic measures in hydrologic data infilling procedures. In: Singh, V.P. & Fiorentino, M. (Eds) Entropy and energy dissipation in water resources, Kluwer Academic Publishers, The Netherlands: 175–192. Shannon, C.E. & Weaver, W. 1949. The Mathematical Theory of Communication. University of Illinois Press Urbana, Chicago, London. Singh, V.P. 1998. Entropy as a decision tool in environmental and water resources. J. Hydrology , Indian Association of Hydrologists, 21(1–4):1–12. Singh, V.P. & Florentino, M. 1992. A historical perspective of entropy applications in water resources. In: Singh, V.P. & Fiorentino, M. (Eds) Entropy and energy dissipation in water resources, Kluwer Academic Publishers, The Netherlands: 21–61. Singh, V.P. & Krstanovic, P.F. 1987. A stochastic model for sediment yield using the principle of maximum entropy. Water Resources Research, 23(5):781–793. Stephenson, D. 2002. “Modular kinematic model for runoff simulation”. In: V.P.Singh, & D.K.Frevert (Eds). Mathematical models of small watershed hydrology and applications. Water Resources Publications, LLC, pp. 183–218, Chapter 7. Yang, Y. & Burn, H. 1994. “Entropy approach to data collection network design”. J. Hydrology, 94:307–324.


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Yevjevich, V. (1972). Probability in hydrology. Water Resources Publications, Colorado, U.S.A.: 331.

Data collection experiences in water level monitoring, borehole archive and research projects in semi arid Botswana Magowe Magowe, Thothi Obakeng & Paul Makobo Department of Geological Survey, Hydrogeology Division, Lobatse, Botswana Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: The Department of Geological Survey (DGS) of Botswana has been carrying out water level monitoring of non-operational wellfields since 1983 and various research projects throughout the country. This involved intense collection of data on water levels and rainfall manually and later on automatic data collection instruments were introduced. This data was stored as hardcopies without quality assurance. Problems experienced with this data collection encompass logistical, equipment and human input. The logistical problems include poor accessibility due to the country’s hostile environment such as dust and extensive ponding during heavy showers. This hostile environment leads to reduction of the lifespan and the poor performance of these instruments. Poor handling of data, equipment failure, lack of the right set of equipment and local operational knowledge also poses problems. Therefore, as a consequence, valuable data is normally lost. In 2003, a quality assurance process was resumed for the 1999–2003 water level monitoring and rainfall records. Common problems that were encountered are data gaps which could be explained by the above causes. During the quality assurance of 1999–2002 data for the ten (10) monitoring network areas, data gaps or unavailable data constituted 80% of all recorded problems (DGS, 2003). This paper discusses the experience of the DGS in collecting hydrogeological data in Botswana semi arid environment.

1 INTRODUCTION The DGS Hydrogeology division has been collecting data in the areas of monitoring, borehole archive and research projects. Data collection in monitoring started in 1983 and since then boreholes from various groundwater projects have been added to the

Data collection experiences in water level monitoring, borehole archive and research projects

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monitoring network. The data serves various purposes such as establishment of benchmarks and parameters of various systems. Monitoring is comprised of water level and rainfall measurement for establishing the natural piezometric surface. Knowledge of the natural piezometric surface is also needed as an input in water resources modelling and groundwater recharge estimation efforts. National Borehole Archive acts as storage for all borehole data whereas Research projects collects data on various hydrogeological parameters. This data collection is wrought with problems that are of logistical, equipment and human nature. 2 MONITORING Water level measurement by manual dipping and change of rainfall charts are done on monthly basis in selected boreholes. The problems recorded in the data collection sheets of ten monitoring networks are depicted in Figure 1.

Figure 1. Distribution of problems as recorded in water level records for 1999–2002 period. 3 MONITORING LOGISTICAL ISSUES However, this schedule is not followed due to several problems such as poor accessibility due to the country’s hostile environment and its vastness. Since the present monitoring network is determined by the groundwater potential projects carried out, most of the monitored areas are in remote areas far from the main office and are laden with heavy


38

sands and muddy soils from heavy thunderstorms. This means that a four wheel drive vehicle is a necessity. However, in some cases these vehicles are not available and this results in data gaps for some months. The other problem is late availability of transport which results in the late changing of water level/rainfall charts and water sampling. This renders the data useless as it results in the superposition of more than one line on the charts making it difficult to read. In some cases, other stakeholder dealing with water connect these monitoring boreholes to water supply out of emergency to supply people with water and this creates data gaps in the records as the borehole will not be accessible and cannot be used. In other cases, other water authorities drill production boreholes adjacent to these monitoring boreholes and the pumping creates interference and as such the borehole will be taken out of the network. Some of the boreholes are in private property and in some cases there is no access as the gates are locked. In other situations the dipper is reported to be stuck for the whole year such as in borehole 6736 in Lethakeng/Bothapatlou monitoring network. 4 MONITORING DATA COLLECTION ISSUES 4.1 Recording One of the major problems is the recording system. There are several problems associated with data recording and these include the following: – Unclear or no comments, this include things such as reporting same borehole dry and blocked/ collapsed for different months or reporting “no hole for dipper” – Water level taken from a borehole with unknown number – Incorrect entry of measured values – Measured values being different from the chart recorded value. This unclear recording resulted in data being discarded hence creating data gaps. 4.2 Quality check All the collected data between 1999 and 2002 was just filed without being checked and the lack of quality check was evident by a lot of problems encountered during the quality assurance of this 1999–2002 data. This lack of timely quality checking resulted in some data points being thrown out as it was difficult to know the exact reasons for these discrepancies/anomalies. This included problems such as recording problems. 4.3 Data storage Until 2003, all the collected hard copy data was not being digitised and it was not filed properly. The records/charts were either misfiled in different binder or thrown in drawers. This resulted in some of the records missing and these added to the issue of unavailable data.


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4.4 Equipment Lack of proper preparation for the field also creates data collection problems. In some cases, it is reported that dipper or its light was not working and this results in partial or no data collection. Due to lack of timely quality check it becomes difficult in ascertaining the source of the mal/non-functioning of the equipment, whether it is the sensor or the batteries. The other problem was from the mechanical water level recorders being used, these were perceived as a better replacement of manual dipping, and however, they came with their own shortcomings. In most cases, the monitoring equipment used was designed and manufactured in Europe where the environment is completely different from the semi arid conditions of Botswana. This has lead to tremendous reduction of the lifespan and the poor performance of these instruments. Some of the problems experienced include – Stuck pens rendering the data – No marking on the chart resulting in blank chart.

5 MONITORING HUMAN RESOURCES ISSUES 5.1 Knowledge In most cases, the personnel operating some of the equipment such as water level recorders, dippers, sampling pumps and rain gauges lack the technical know-how necessary to implement first line maintenance. This result in late or no acquisition of data and hence data gaps develop while the equipment is sent for maintenance or replacement. The lack of knowledge sometimes results in the equipment not being calibrated or set up properly and this indicated off scale water level and rainfall curves. 5.2 Availability The personnel used for data collection are at technician and artisan level. In most cases these personnel are shared among the various on going research projects and the normal monthly monitoring. This results in one of these activities suffering due to nonavailability of the personnel for a certain period and as such data gap will be inevitable. 6 NATIONAL BOREHOLE ARCHIVE (NBA) NBA records borehole data on daily basis. This includes registering privately drilled boreholes; entering borehole data in the database including plotting boreholes on hardcopy maps and storing rock chip samples. 6.1 NBA Logistical issues There are several logistical problems associated with NBA. One of these problems is the running out space for rock chip samples storage. The lone core shed is full and this has resulted in the new and reliable samples being piled without proper storage. The other


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problem is the use of outdated topographical maps for plotting boreholes which results in difficulty in borehole location verification. The lack of physical verification of registered boreholes is also one of the problems. This is due to the fact that boreholes are drilled almost daily all over the country and due to its vastness; it is difficult to cover all the drilled boreholes. 6.2 NBA Quality check Since the NBA is the storage for all drilled boreholes in the country, the issue of data quality check is very important. However, until recently it has been neglected especially on the privately owned boreholes. As an authority responsible for registration of private boreholes, one of the main tasks is to verify the location of the boreholes as provided by the owner/driller so that the borehole could be plotted correctly in the map. However, this has not been done adequately and as such a lot of boreholes have uncertain location. 6.3 National Borehole Archive Human Resources issues 6.3.1 Availability The personnel used for data collection are at technician and artisan level. In some cases these personnel is shared between NBA and the normal monthly monitoring. This results in one of these activities being suspended for a certain period and creating backlog. 7 RESEARCH PROJECTS (RP) The Hydrogeology division has been running various projects ranging from groundwater potential survey to hardcore research projects such as Groundwater Recharge Evaluation Studies (GRES) and the Kalahari Research Project. These projects are multi-disciplinary and use different equipment and collect different data sets. In most cases these projects are carried out jointly with external partners and therefore timely bound. These projects, especially those run in-house experience a lot of problems. 7.1 Research Projects logistical issues In most cases these projects are carried out in remote areas and several problems are experienced in the field. This includes transport problems such as vehicle breakdown which takes a long time to fix due to the long process to be followed. In some cases there is a need to seek permission from other stakeholders and these requests can result in extension of the program while waiting for approval. This includes funds approval and changing the scope of the study. For example, the approval of funds and changing of project scope may take three (3) to four (4) months of valuable field activity time. This negatively affects projects that require time based data.


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8 RESEARCH PROJECTS HUMAN RESOURCES ISSUES 8.1 Knowledge In most cases these projects use specialised equipment that requires special operating level. However, most of the personnel have never been exposed to this equipment and this can result in loss of data or collection of unreliable data. For, example various software used to operate Skye data loggers are still unknown to a good number of hydrogeological technical personnel within Hydrogeology Division. 8.2 Availability The personnel used for data collection are at technician and artisan level. In most cases these personnel is shared among the various on going research projects and the normal monthly monitoring. This lack of technical level staff impacts negatively on the running of these projects. This results in the project using unqualified staff to fill the gap; however, that has serious implications on the quality of the collected data. In other situations, there is a need to have specialised personnel such as a welder to develop a specialised piece of equipment on site. This can result in delays especially if that person is unavailable or is occupied with other departmental work. 8.3 Equipment Some of this necessary specialised research equipment needs special care and due to harsh conditions prevailing in these remote areas, a lot of time is lost when the equipment breaks down since it must be sent overseas to be fixed. This also results in loss of data especially temporally dependent data. 9 CONCLUSION On the basis of this experience, we conclude that the following aspects are vital for a successful and reliable hydrogeological data collection effort in the semi-arid Botswana environment. – Routine analysis of the archived data should be a must rather than an option, in order to eliminate useless data before it accumulates in large amounts within records. – Routine training programmes for technicians on field equipment should be designed to enable technicians to keep abreast with the changing technology that is specific for hydrogeological applications. – Increasing manpower capacity by recruiting personnel with basic hydrogeological monitoring and database knowledge in order to facilitate data collection and reduce data losses arising from lack of knowledge. This will increase the reliability of the collected data. – The general public and other stakeholders need to be informed about the importance and relevance of hydrogeological research, borehole archiving and monitoring


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activities, so that they can allow such activities in their private properties such as farms. – Manufacturers must be encouraged to design field equipment suited to the hostile semi arid and saline conditions of Botswana, so that the durability of the field equipment can be guaranteed. – Periodical inspection of water level monitoring boreholes should be a must in order to curtail issues of “dry” or “blocked” boreholes, hence maintain a continuous and an accurate water level record. – A comprehensive process map of water level monitoring program which include recording of the environmental status or changes in the vicinity of the monitoring borehole such as new pumping borehole. – Conduct a routine water sampling of observation boreholes. Currently the Hydrogeology Division is engaged in improvement of data collection and archiving through implementation of the following programs. – Acquisition of digital water level and rainfall recorders and accessories to replace mechanical ones and manual dipping. This will reduce human errors and improve data quality. – Development of proper databases and checking data immediately from the field to ensure that issue of unclear comments and data anomalies are reduced hence maintaining good quality data. – Development of process maps to improve the quality of the data being collected and being entered into the databases. This will ensure that all factors are considered before a inexplicable conclusions such as “dry” boreholes are reached. – Field programs are being carried out to review borehole location maps. This is to ensure that borehole locations are correct and indeed the plotted boreholes do exist. Regular data collection even if it is not part of a specific study, helps to build a picture of the general behavior of the system. The data collected provides valuable comparisons and context when the system is studied in more detail. However, all this will not be possible if the data collected is wreaked with a lot of problems. REFERENCES Department of Geological Survey. 2003a. Groundwater Monitoring of Non-Operational Wellfields and Other areas of Development Interest, compiled by T.Kellner, vol. 1b–1d. Department of Geological Survey (2003), Groundwater Monitoring of Non-Operational Wellfields and Other areas of Development Interest, compiled by T.Kellner, vol. 2b, 2d–2f, 2h–2k.

Rainfall characteristics in semi-arid Kitui district of Kenya A.O.Opere, V.O.Awuor, S.O.Kooke & W.O.Omoto Department of Meteorology, Nairobi, Kenya Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: Variable semi-arid climate characterized by precipitation patterns unfavorably distributed in space and time and high evaporation rates reaching up to 100% of the incoming monthly precipitation is a challenge facing water resources management in arid and semi-arid lands (ASALs). Kitui district in Kenya is an example of an ASAL environment where water resources management issues are particularly important and sensitive. Sources of water are nearer to the people in the wet season, but as the seasonal rivers dry up, distance to water points get as far away as 25–30km. There is, however, great potential for rainwater harvesting. This is dependent on proper understanding of the patterns of precipitation both in space and time. This would be useful in understanding drought characteristics in order to develop strategies to capture, store and redistribute the available water. The spatial characteristics were determined through principal component analysis (PCA). Season lengths, drought severity and frequency were determined. The results indicated that, on average, the onset for the long rains (March–May) was centred on day 82.36 while cessation was on day 126.3. The longest season was 107 days during the long rains while the shortest lasted 7 days during the short rains (October–November). Severe droughts in the district were experienced in 1980, 1985, 1990 and 1995. The largest seasonal total for the long rains was 768mm with a return period of 25.9 years while the smallest total was 81.1mm with a return period of 1.0 years. For the short rains, the largest total was 1022.0mm with a return period of 15.7 years and the smallest total was 205.4mm with a return period of 1.0 years.

1 INTRODUCTION Efficient and sustainable use of available water resources is paramount for a peaceful, sustainable and equitable development of any region. Some of the challenges to integrated and sustainable water resource management include:


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Changing land use, land degradation by erosion, deteriorating water quality and competing water demands by stakeholders. There exists, therefore, a strong demand for an integrated water allocation and decision support system. The backbone of such a system must be scientifically sound to be accepted and trusted by stakeholders. Efforts to improve catchment management and to impose a sustainable water resources management are of economic and political importance for any country. Variable semi-arid climate characterized by precipitation patterns unfavorably distributed in space and time and high evaporation rates reaching up to 100% of the incoming monthly precipitation is a challenge facing water resources management in arid and semi-arid lands (ASALs). Kitui district in Kenya is an example of an ASAL environment where water resources management issues are particularly important and sensitive. Sources of water are nearer to the people in the wet season, but as the seasonal rivers dry up, distance to water points get as far away as 25–30km. The main problems in water development and management in this district include: ● unreliable rainfall and inadequate supply to meet the demand, ● the available water resources are unevenly distributed and inaccessible to all, ● traditional farming methods lack water conservation principles, ● most of the water projects have since been abandoned, and ● High rates of potential evaporation on the available water resources. There is great potential for rainwater harvesting. This is dependent on proper understanding of the patterns of precipitation both in space and time. This would be useful in understanding drought characteristics in order to develop strategies to capture, store and redistribute the available water. Droughts have been the phenomena of great concern throughout the continent of Africa, because of the devastating effects they have inflicted on the economies of some of the countries in the continent. Kitui District located in Eastern Kenya is no exception and is an example of one of the most vulnerable areas to the effects of drought. Droughts are usually classified as meteorological, hydrologic or agricultural depending on the variable under investigation. Definition of droughts has also been given on the basis of theory of runs and stationary structure of time series, Yevjevich (1967). The most important variable in meteorological drought is rainfall, in hydrological drought is availability of water in rivers, lakes, reservoirs, and ground water resources; and in agricultural drought is the soil moisture content to sustain the crop growth. Drought analysis involves investigation of duration, magnitude or severity, frequency and regional spread of the event. There have been limited investigations on meteorological droughts in Kenya. However, substantial work exists on the drought characteristics for the various agro-climatic regions of South Africa; Dyer and Tyson (1977), Zucchini and Adamson (1984), Dent et al. (1987). The study investigates the duration, magnitude or severity as well as frequency aspects of drought within Kitui District.

Rainfall characteristics in semi-arid Kitui district of Kenya

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2 DATA AND METHODS 2.1 Data: types, sources and problems 2.1.1 Historical data Historical data from thirteen rainfall stations within and around the project area were analyzed. The first part of this analysis was to determine the onset and cessation dates of rainfall in each year for the short and long rains. The duration for each season was then derived. 2.1.1.1 Filling in missing records Many rain gage records are incomplete. It is necessary to estimate the missing data in order to utilize partial records, especially in data sparse areas. The methods used include: ● Arithmetic average method ● Normal ratio method ● Correlation method ● Inverse distance method The problem of filling data at un-gauged location involves transmitting data at the nearby index gages to the un-gauged location. The missing data can be formulated as (1) ai is the weighting factor of the ith gage with record Pi and N is the number of index gages while Px is the rainfall to be estimated at x. The different methods differ in their methods of estimating ai’s where i=1, 2,…………………N 2.1.2 Data quality control One of the sources of error in rainfall measurement is the location of the gage in relation to obstructing objects such as trees and buildings. In the progress of time, trees grow and buildings come up. This means raingages must be moved. This may affect the consistency of the records from the raingage i.e. the records before and after the movement might be different. In addition, change in observational procedure might also affect the consistency.


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Inconsistency in a rainfall record may be detected by graphical or statistical methods such as double mass analysis, the Vonn Neumman ratio test, cumulative deviations, likelihood ratio test and runs test. 2.2 Methods 2.2.1 Principal component analysis (PCA) The method of PCA involve the transformation of a greater number of unorthogonal (manifest) variables into smaller number of orthogonal variables, which present common causes of manifest variable changes. It can therefore reduce the dimensionality of a problem by replacing the measured variables and the inter-correlated variables by using a smaller number of uncorrelated variables. This can be useful in reducing the amount of basic data to be processed. Depending on the data, it is possible to interpret the orthogonal functions in terms of some underlying physical processes. Castell (1966) proposed a method of retaining significant factors in PCA solutions. Similar methods have been used by Ogallo (1988a,1989) and Basalirwa et al. (1995) for East Africa and Tanzania respectively. This method was used to group rainfall records from the study catchment into homogeneous zones. Mathematically, a variable Z may be transformed in terms of m common empirical orthogonal function (factors) and n unique factors as below: (2) where, Zi is variable i in the standardized form Fi represents the common orthogonal vector (factor) ui is the unique factor for variable i ai1=standardized multiple regression coefficient of the variable i on the common factor 1 (factor loading). The unique term diui=0 since principal component analysis does not consider the unique component of the variance. Details of this method are available in many referencesincluding Drosdowsky (1993), Ogallo (1989) and Basalirwa (1991) among others. 2.2.1.1 Identification of representative rainfall station Principal component analysis (PCA) solutions were used to identify the most representative station in the area of study. This formed the basis for further analyses including onset/cessation of rainfall, dry spell lengths and frequency. Two stations from the thirteen stations were chosen for detailed analyses. These were Kitui Secondary School (identified as station with highest communality from PCA results); thus is a representative station based on communality concept. Kitui Water Office was also used for comparison of results.


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2.2.2 Drought indices Drought duration is a crucial component particularly if one has to plan for storage that can last certain duration of drought for given water demand. The duration portrays the season lengths hence the potential success or failure of a water supply scheme that can be put up. At each of the stations, the onset and cessation dates were determined for each year and for each season i.e. long and short rains. The actual, earliest and latest onset and cessation dates was the basis of deriving average, shortest and longest duration at each of the stations. Mhita (1990) has made similar attempt in Tanzania. Two methods used were the water balance technique and pentad method. Both methods are based on preset hydrological conditions, to determine the onset and cessation of rainfall. Details of these methods are briefly discussed in the following sections. 2.2.3 Pentad method Definition of the start of the rains that is used is based on preset hydrological conditions. The first occasion after March 1st and October 1st that the running 5 day total exceeded 25mm and there being no dry spell exceeding 7 days in the next 21 days (Successful start, threshold of 1mm). In a nutshell, the pentad method involves computing a 5-day total rainfall for each year. The cumulative values of the 5-day total are divided by the annual total for each year and expressed as a percentage, that is, ΣPi*100/Annual total. These are plotted against pentad numbers. The onset and cessation dates are then determined from the plots. 2.2.4 Water balance technique The first occasion after March 1st and October 1st for the long and short rains respectively when the water balance goes to zero (capacity 100mm, daily evaporation 6mm). A water balance approach was used with a threshold of 1mm of rainfall. Evaporation rate for the area is taken to be 6mm per day on average. The soil moisture capacity was taken to be 100mm (i.e. average soil moisture during dry days). No runoff is generated since the rainfall amounts cannot even satisfy the evaporation demand. 2.2.5 Determination of season duration The maximum duration for each season was obtained using the earliest onset and latest cessation for the period of study in each of the two stations. The longest and shortest duration for each season was also determined for the two stations. 3 RESULTS AND DISCUSSIONS The results of the PCA, onset/cessation of rainfall, dry spell lengths and frequency are presented in the following sections.


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3.1 Results of the principal component analysis From the results, three Eigen vectors were retained based on the Scree method (see Fig.1).

Figure 1. Scree test of Castell. Kitui Sec. School had the highest communality and was thus picked as the most representative station for further analysis. Results from PCA can be seen in Table 1 and Figure 2. The spatial map was obtained by mapping the factor loadings at the station locations. Three homogeneous regions were delineated from these results indicating complex rainfall variability within the study area.

Table 1. Rotated loading matrix. Variable (rainfall stations) 9137012 9137010 9137003 9138000 9137020 9137028 9137045 9137058 9137073

Factor 1

2

3

0.212 0.0373 0.164 0.458 0.191 0.385 0.757 0.274 −0.027

0.288 0.119 0.154 0.122 0.786 0.293 0.179 0.531 0.141

0.325 0.656 0.643 0.549 0.171 0.396 0.331 0.251 0.770


9137076 9137094 9138003 9138013 Variance explained % of total Variance

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0.796 0.196 0.056 0.063 0.792 0.082 0.848 0.129 0.106 0.546 0.147 0.256 2.908 1.876 2.290 22.37 14.429 17.612

Figure 2. Homogeneous rainfall zones of Kitui. Table 2. Examples of onset/cessation dates. Average Earliest/shortest Latest/longest Std. (Day (Day no.) (Day no.) dev. no.) (Day no.) 9137012 LR onset LR cessation LR duration SR onset SR cessation

96.9 131.4

76 115

123 11.84 141 8.19

35.45

7

56 11.37

307 342.2

280 333

335 12.89 366 8.483


SR duration 9137010 LR onset LR cessation LR duration SR onset SR cessation SR duration 9137003 LR onset LR cessation LR duration SR onset SR cessation SR duration 9138000 LR onset LR cessation LR duration SR onset SR cessation SR duration

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36.18

11

69 17.31

82.35 143.1

0 124

122 25.21 163 10.04

62

18

149 30.68

306.9 349.4

287 328

319 9.462 366 12.45

46.17

14

76 19.04

93.7 138.4

64 122

129 16.35 152 6.905

46.05

11

83 20.02

307.8 342.3

289 336

324 10.26 361 8.42

37

16

71 15.02

97.92 124.5

78 99

144 14.44 172 16.38

27.63

8

47 12.15

316 353.8

296 336

341 12.51 366 11

41.13

6

60 15.66


Figure 3. Water balance for Kitui Water Office.

Figure 4. Pentad for Kitui Water Office 1989.

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Figure 5. Water balance for Kitui Sec. School—1984. 3.2 Onset and cessation dates of rainfall Some results for onset/cessation dates and season duration are given Table 2. A few examples of the results from pentad method for the two stations are given in Figure 4 and Figure 6. The annual water balance plots from the water balance technique is also given in Figure 3 and Figure 5.

Figure 6. Pentad for Kitui Water Office 1988.


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Table 3. Dry spell lengths for Kitui Sec. School and Kitui Water Office. Kitui Sec. School Year L S 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998

22 31 27 24 35 27 84 18 36 66 32 81 69 70 33 8 55 61 37 12 14 23 7 16

Kitui Water Office Year L S

18 1981 23 1982 39 1983 155 1984 18 1985 79 1986 23 1987 14 1988 169 1989 9 1990 17 1991 149 1992 83 1993 41 1994 18 1995 12 1996 15 1997 27 140 11 13 114 107 26

11 10 23 8 13 56 31 43 18 22 70 46 20 5 7 114 7

12 17 25 67 30 13 72 28 47 17 72 64 28 26 31 23 107

The two methods were found to be comparable. For example, Kitui Water Office: Average onset of long rains is on day 82.36 and cessation on day 126.3 using the two methods. On the other hand onset is on day 84.37 and cessation on day 137.5 using the pentad method. These results are also presented in Table 2.


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Figure 7. Dry spell lengths during long rains—Kitui Sec. School.

Figure 8. Dry spell lengths during short rains—Kitui Water Office. 3.3 Season lengths/duration Some of the results of the season lengths for Kitui Water Office and Kitui Sec. School are given in Table 4 and presented in Figure 7 to Figure 10. From the results in Table 4, for instance, Kitui Sec. School shows the longest long rains duration in 1997 (107 days). The same year also shows the shortest short rains duration (7 days). The result is confirmed in Kitui Water Office for the year 1997.


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3.4 Drought severity This was based on the anomalies of the seasonal totals for each year for the two stations. A normal expectation was taken to be ±0.5 s.d. For Kitui Water Office, 1985, 1990 and 1995 were severe in terms of the long rains totals. The same years are also severe for the short rains. In Kitui Sec. School, 1980, 1985, 1990, 1995 were severe during the long rains as well as during the short rains. The seasonal totals for the very dry years can be used as a basis for planning for a water storage facility. Examples of the anomalies are given in Figure 11 and Figure 12.

Figure 9. Dry spell lengths during long rains—Kitui Water Office.


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Figure 10. Dry spell lengths during short rains—Kitui Sec. School. 3.5 Drought frequency Gamma distribution was used to fit the seasonal totals for the period of study. The results are shown in Figures 11–12 and Table 4, while Figure 13 indicates the gamma distribution. In Kitui Water Office (KWO), the largest seasonal total for the long rains is 768.3mm and has a return period of 25.9 years. The smallest seasonal total is 81.1mm with a return period of 1.0 years. For the short rains, the largest total is 848.6mm with a return period of 20.1 years and smallest total is 98.76mm with a return period of 1.0 years. In Kitui Sec. School (KSS), the largest seasonal total for the short rains is 1022.0mm with a return period of 15.7 years while the smallest seasonal total n is 205.4mm with a return period of

Table 4. Values expected frequency MAM(KWO) OND(KWO) Gamma dist. Gamma dist. Mean 344.1 & Mean 441.2 & k of 2.929 k of 4.133 8µM and decreased towards offshore. A similar trend was observed for ammonia-N with the source centered on Chethi (at about 15m depth). It may be assumed that the ammonia released were either rapidly utilized by phytoplankton or oxidized within the system itself where the waters were saturated with dissolved oxygen. Distribution of silicate-Si was similar to that of nitrate (4–10µM), higher than the corresponding values reported for the waters of Southeastern Arabian Sea. The input of these nutrients supported high primary production up to 14mg/m3 of chlorophyll a (peak column production of


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Figure 2. Distribution of ammonia-N (A), nitrite-N (B), nitrate-N (C) phosphate-P (D) at the surface and bottom during October (a, b), February (c, d) & November (e, f). 1529mgCm2d−1), approximately 3 times greater than the peak values reported so far from these waters Qasim et al (1978). The peaks in chlorophyll a and ammonia showed a preference of ammonia among the nutrients for primary production. It is difficult to point

Subterraneous injection of nutrient rich groundwater to the coastal waters

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out a definite source to these high nutrients during this period, as the fresh water discharge was at the minimum.

Figure 3. N/P peak values funneling out from mud bank region.


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During post monsoon (November), homogenous mixed layer prevailed in the entire region. While the physical characteristics were more or less stable, there was considerable variability in the nutrients and in chlorophyll a concentration (Fig.2 A–D). A marked decrease in sub-surface dissolved oxygen (2.8–4.8ml/l) was the characteristic feature of this period, which was concomitant with enriched nitrite (0.5–2.0µM), phosphate (0.4–2.8µM) and silicate (0.5–14µM). The ammonia (1–7µM) and nitrate (1– 6µM) were also elevated at some regions along southern transects. The enriched particulate organic carbon (>3.5mg/l) and Chlorophyll a (14.8mg/m3) were also the notable features of this period. It is likely that chlorophyll a values were proportionate to carbon production indicating a strong positive relationship binding it with nutrient related factors rather than seasonal or diurnal fluctuation. The elevated nitrite and phosphate levels around Cochin may be due to the input from the backwaters. Higher values of nitrite, POC and chlorophyll a towards the southern offshore waters off Pallana were conspicuous and the regions with high nitrite had nitrate levels up to 6µM and the low levels of ammonia had ruled out the nitrification as a significant process responsible for nitrite accumulation. The remarkable co-existence of nitrite with nitrate strongly suggested that the nitrite production should mostly be due to assimilatory reduction. This was further substantiated by the high concentration of chlorophyll a (4–9.8mg/m3) on these transects. The N/P ratio in the coastal waters was below 15 during November (Fig. 3), possibly due to the disproportionate release of P from mudbank sediment. However, a band of N/P>15 funneling out from Alleppey region was indicative of an ‘external source’ of nitrogenous compounds into the coastal waters. A comparison of long-term (decadal) trend in the chlorophyll data of this region showed “greening” of near shore waters Devassy (1983). This suggests that phytoplankton standing crops had increased historically, possibly in response to watershed nutrient inputs. These sources of nutrients deserve identification as it was traced to a region, far away from any river mouths. The current observations in general indicated the presence of a nutrient source between Chethi and Pallana. This region has mud banks but the release of nitrogenous compounds cannot be accounted from sediments. The injection of nutrients was in nonmonsoon months when mud banks were passive and a new influence of Vembanad Lake on the coastal waters is very clear. One of the recent estimate shows that in spite of receiving 42.4×103mold−1 of inorganic phosphate and 37.6×103mold−1of inorganic nitrate from Periyar side of the estuary, the export to the coastal waters is only 28.2×103mold−1of inorganic phosphate and 24×103mold−1 of inorganic nitrate Naik (2000) and the lake acts as a sink for the nutrients, flushing out only a portion of the pollution load that it receives. Increased human population along the coastal belt has also resulted in concomitant increases in widespread use of septic tanks and nutrient inputs to coastal waters, particularly from regions occupying limestone beds. It has been found that domestic wastewater from septic tanks provide more nitrogen than that due to precipitation or use of fertilizers. The situation is exacerbated in the present study region, as more than 70% of households in these coastal belt and adjacent areas of Vembanad Lake do not have proper sanitation facilities. Significant amounts of nutrients from fertilizer applied in agricultural fields (approx. 94kg/ha) leach out into waterways, groundwater and to the coastal bays inducing coastal fertilization due to direct discharge into coastal ocean and through ground water seepage.

Subterraneous injection of nutrient rich groundwater to the coastal waters

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3 CONCLUSIONS The nutrient fluxes into coastal region were influenced by fluxes from Cochin backwater and by the mud bank formation. The present study isolates a possible link between Vembanad Lake that supplies primary nutrients to the adjacent coastal waters and precondition it for rich primary production during non-monsoon months. The causative factors discussed are indicative of existence of a subterranean flow connecting Vembanad Lake to the adjacent coastal waters through the submerged porous lime shell beds. Continuous nutrient entry through such process is bound to upset coastal water productivity pattern. If the existence of the subterraneous channels linking Vembanad Lake to the adjacent coast is proved, it might even re-construct the historical evidence that the subterraneous flow plays a decisive role in the formation of mud banks along this region. A sub aqueous injection of nutrients into the coastal waters through this region is possible even after the rainy season. This assumption need further study to establish cause and affect mechanisms and quantify actual trends created by increased nutrient loading. REFERENCES Anonymous, 1996. Pollution potential of industries in coastal areas of India. Coastal Pollution Control Series: central Pollution Control Board Report. COPOCS/9/1995–96. Anonymous. 1998. NEERI- carrying capacity based developmental planning of Greater Kochi Region. Phase I Report. Devassy, V.P. 1983. Mahasagar, Bull Bull Nat. Inst. Oceanogr.7:101–105. Hema Naik, 2000. Budgets for Periyar estuary, Kerala. Presented at Regional Training Workshop on Biogeochemical Budgeting and Socio-Economic modeling for Coastal Scientist. APN/SASCOM/LOICZ, 18–22 September, Colombo. Jayakumar D.A., Naqvi S.W.A., Narvekar P.V. & George M.D. 2001. Methane in coastal and offshore waters of the Arabian Sea. Mar. Chem. 74:1–13. Mathupratap N.M., Prasanakumar S., Bhattathri P.M.A, Dileepkumar M., Reghukumar S., Nair K.K.C. & Ramaiah N. 1996. Mechanism of the biological response to winter cooling in the north eastern Arabian Sea. Nature, 384:549–551. Nair C.K., Balchand A.N. & Nambisan N.P.K. 1991. Heavy metal speciation in sediments of Cochin estuary determined using chemical extraction techniques. Sci.Total Environ. 102:113– 128. Naqvi S.W.A., Jayakumar D.A., Narvekar P.V., Naik H., Sarma V.V.S., D’Souza W., Joseph S. & George M.D. 2000. Increased marine production of N2O due to intensifying anoxia on the Indian continental shelf. Nature, 408:346–349. Qasim, S.Z., Wafar, M.V.M., Sumithra Vijayaraghavan, Joseph P., Royan. & Krishna Kumari, L. 1978. Ind. J. Mar. Sci.,7:84–93.

A new method for the estimation of episodic recharge J.Bean, G.van Tonder & I.Dennis Institute for Groundwater Studies, University of the Free State, Bloemfontein, South Africa Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: A new stable isotope-based technique, the Modified Amount Effect (MAE) Method, was developed during this study. This technique provides insight into episodic recharge processes by estimating the proportion of preferential pathway-to-matrix-derived flow entering an aquifer, and the amount of rainfall required to initiate recharge via the respective flow paths. Significantly, the proportion of bypass flow can be determined without undertaking expensive and time-consuming unsaturated zone studies, both factors often of primary concern when undertaking recharge investigations in developing countries.

1 INTRODUCTION There can be no doubt that the South African water industry has been profoundly transformed over the last 10 years, with millions of rands invested in water infrastructure aimed at ensuring that every South African has access to fresh drinking water. In drier, more isolated, inland areas of the country, this has often meant that available groundwater resources must be exploited. As such, government and non-government organisations have invested in research associated with developing new assessment techniques so that these resources can be managed sustainably. In common with all these strategies is the need for recharge processes to be understood, and if possible, quantified. An understanding of site recharge behaviour is far more important than many geohydrologists realise, and goes beyond estimating the average proportion of rainfall entering a given aquifer. For example, from a planning viewpoint, groundwater ingress into a mine is seldom problematic to mine management, providing it is constant; problems occur when unpredicted increases occur, such as those associated with the sudden entry of recharge water into surrounding aquifers. Thus, through understanding the episodic nature of recharge in semi-arid and arid areas, and therefore the thresholds that must be exceeded before recharge occurs, geohydrologists are better able to provide predictive advice for their clients. This paper discusses a new stable isotope-based

A new method for the estimation of episodic recharge

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technique, the Modified Amount Effect (MAE) Method. This was developed during the study, which provides insight into episodic recharge processes. 2 THE MODIFIED AMOUNT EFFECT METHOD 2.1 General This technique provides insight into episodic recharge processes by estimating the proportion of preferential pathway-to-matrix-derived flow entering an aquifer, and the amount of rainfall required to initiate recharge via the respective flow paths. Significantly, the proportion of bypass flow can be determined without undertaking expensive and time-consuming unsaturated zone studies, both factors often of primary concern when undertaking recharge investigations in developing countries. 2.2 The Methodology Recharge water is progressively enriched in δ18O due to evaporation, which occurs with movement through the unsaturated zone. The slope of the evaporated water line for matrix water in the unsaturated zone (EWL-U) is generally around 5, but sometimes as low as 2. The variable d was corrected to represent evaporation within the unsaturated zone by constructing a line through the 2H and 18O average for those samples representing background recharge (i.e. δ18O10L/s) often occurring at the structure/sediment interface. These have been locally overlain by calcretes to a maximum depth of about 15m. Petrusburg has a semi-arid climate, with an evaporation excess of 1920mm (2380– 460mm MAP) annually. Given that the water table is generally less than a metre below the pan surface, groundwater here is exposed to continuous evaporation in most years, the exception being those years where sufficient rainfall occurs to flood the entire pan for a few months of the wet season. Thus, the slope of EWL-U in these areas should be parallel to GWL because, while preferential pathway-derived water may not be as evaporated as matrix-derived during recharge events, it will eventually be evaporated to the same degree after entering the aquifer. Liebenberg’s Pan-derived brine with chloride concentrations in excess of 100000mg/L is further concentrated in evaporation ponds that have been constructed on site as part of a commercial salt-extraction enterprise operated by a local farmer. The pan itself is the lowest topographical feature in the landscape. Land use varies with soil type, topography, and access to irrigation water, with grazing and dairy farming predominant to the north and west of the pan in the steeper dolerite hills that occur there, and irrigated cropland located to the south and east on deeper soiled, gently sloping ground. 2.3.2 Calculating recharge using MAE The orientation of the EWL determined from brine samples was determined to be δ2H= 3.65 δ18O+−4.71 (refer to Figure 1). Another characteristic of Petrusburg data of interest is that evaporation-induced enrichment has not been excessive as would be expected in this type of environment, with all groundwater samples having a δ18O concentration 3.3‰ or less. This suggests that brine has mixed with isotopically depleted water from another source, the most likely being groundwater from upslope areas, a finding


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supported by the occurrence of freshwater springs at various locations around the perimeter of the pan, and the observed decrease in brine concentrations in production bores over time. PPflow estimated using the MAE Method is between 33 and 25% assuming an EWL-U slope of 3.65.δ18O and 2.5.δ18O, respectively (refer to Figure 2). However, given the potential for brine/ fresh groundwater mixing, the lower figure would be more acceptable in this instance. Further insight into site recharge processes can be obtained when variations observed in recharge threshold estimates obtained using the cumulative rainfall departure method (CRD) and MAE techniques are considered. On the basis of 98 years of rainfall data for Petrusburg, the average

Figure 1. Stable isotope characteristics of groundwater samples taken in the vicinity of Liebenberg’s Pan, Petrusburg. “GW”, “PW”, and “Ave” denote groundwater samples taken from boreholes surrounding the pan, in the pan, and the background isotopic average, respectively.


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Figure 2. Line characteristics used to determine PPflow at Liebenberg’s Pan. monthly rainfall is 35.7mm; this value also representing the long-term recharge threshold for an aquifer in equilibrium if seasonal conditions are ignored. In theory therefore, there would be no change in water levels if 35.7mm of rain fell at the site every month. Under field conditions however, this does not occur; prolonged periods of below average rainfall are evident throughout the Petrusburg dataset. Thus, in order to restore equilibrium conditions such that the average recharge threshold again decreases to 35.7mm/month, a given catchment must receive above-average rainfall. This observation is significant because it indicates that, for a given aquifer in a semi-arid and arid area, multiple recharge thresholds will be represented in site water level data. Multiple recharge thresholds that are likely to be of importance include those necessary to induce recharge via: 1. Preferential pathways after a period of below-average rainfall; 2. The matrix after a period of below-average rainfall; 3. Preferential pathways once aquifer equilibrium has been restored; 4. The matrix once aquifer equilibrium has been restored. Each of these recharge thresholds can be approximated using available site stable isotope data by applying the mass balance equation: RTave.δ18ORT−ave={RTlow.(X.δ18ORT−low)}+{RThigh.(X−1)δ18ORT−high} Where, RT=Average recharge threshold expressed as an equivalent rainfall depth (mm); RTlow=Average recharge threshold to be exceeded if recharge via preferential pathways is to occur (mm); RThigh=Average recharge threshold to be exceeded if recharge via the matrix is to occur (mm) and δ18ORT-low=Average δ18O concentration of preferential pathway-derived recharge water (‰); δ18Orw-high=Average δ18O concentration of matrixderived recharge water (‰); and, X=Preferential pathway to matrix proportioning factor. The average thresholds to be exceeded before recharge occurs via the matrix, and preferential pathways. Note that these values represent long-term averages, and not the upper and lower limits of recharge thresholds. These limit thresholds can be calculated,


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however, by considering CRD and long-term average values together. For example, the CRD Method indicates that, for an aquifer under equilibrium conditions, the recharge threshold is approximately 35mm/month. Since, on average, the recharge threshold cannot be lower than this amount, it must represent the average lower recharge threshold. Thus, the respective average lower recharge thresholds can be calculated once the isotopic composition of rainfall for an equivalent depth of 35mm has been estimated from amount effect data. Once the lower and average long-term thresholds for both preferential pathway (RTlowand RTave-pp) and matrix-medium recharge (RTlow-uzm and RTave-uzm), the upper recharge pp thresholds RThigh-pp and RThigh-uzm can also be calculated, i.e. RThigh=2.RTave−RTlow Only 25% of recharge at Petrusburg occurs via preferential pathways. On average, recharge occurs via these pathways in more than 50% of all rainfall events (RTave−pp=56.4%). Therefore in episodic recharge environments, resource managers must ensure that allocated water can be used for the entire period between major recharge events, which where recharge via the matrix predominates, can be significant. Indeed, in many instances it may be more realistic to base groundwater allocations on the proportion of bypass flow-derived recharge entering site aquifers initially, the allocations increasing once aquifer storage, recharge threshold, and recharge event return period characteristics are better understood. 3 CONCLUSIONS Four recharge thresholds can be identified using the MAE Method; the low and high recharge thresholds that must be exceeded before recharge occurs via preferential pathways or the matrix, respectively. These represent threshold limits, the low value only of importance following successive months of wet weather, the high value representing the rainfall that must be received to restore an aquifer system to equilibrium after prolonged dry spells. Once these thresholds are known, the recharge history of a site can be modelled using available rainfall data by adapting the CRD Method. An important finding of modelling undertaken during this investigation is that in those semi-arid to arid areas where most recharge water enters, the aquifer via the matrix, the period of time that elapses between successive rainfall events that exceed the matrix recharge threshold often extends to scores of years. This has significant resource management implications for much of the region, as it indicates that the current approach of basing allocations on average recharge estimates is only justified if sufficient groundwater is available for use over the entire period between recharge events. The MAE Method was found to be sensitive to the recharge history of the site, the returned recharge estimate significantly higher when calculated immediately after recharge via the matrix had occurred. This is not to say that these estimates were incorrect (indeed they were representative of site recharge processes at the time of sampling), but that rainfall in the preceding months should be considered prior to sampling. In general however, sampling should be undertaken near the end of the dry season, which in the summer-dominant rainfall areas of Southern Africa is between


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September and November (allowing for a 30 to 60 days lag time between rainfall and subsequent recharge). REFERENCES Alison, G.B., Barnes, C.J., Hughes, M.W. & Leaney, F.W.J. 1984. Effect of climate and vegetation on oxygen-18 and deuterium profiles in soils. Isotope Hydrology 1983. IAEA Symposium 270, September 1983, Vienna.

Prioritisation of the impacts of pollutants on groundwater flow systems in South Africa I.Dennis, B.Usher & J.Pretorius Institute for Groundwater Studies, University of the Free State, Bloemfontein, South Africa Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: Groundwater pollution can occur, as a result of various activities of man. With increased human settlement and economic development, a range of undesirable waste products are produced which can end up in the environment. If these waste products are not well handled, they can cause pollution of groundwater. The threat caused by undesirable substances on groundwater is recognized in South Africa and measures have been put in place through legislation to protect groundwater from pollution. Although groundwater pollution incidences have been reported countrywide, we do not have an indication of the extent of the problem. The results of the investigation discussed in this paper are therefore geared towards filling the gap in the understanding of groundwater pollution in South Africa’s urban environments. By doing so the principal pollutants can be identified and based on their risk prioritised. This will facilitate better management of groundwater quality through the country.

1 INTRODUCTION Groundwater pollution can occur, as a result of various activities of man. With increased human settlement and economic development, a range of undesirable waste products are produced which can end up in the environment. According to the National Water Act (Act No. 36, 1998), pollution is defined as the direct or indirect alteration of the physical, chemical or biological properties of a water resource so as to make it— 1. Less fit for any beneficial purpose for which it may reasonably be expected to be used; or 2. Harmful or potentially harmful— ● to the welfare, health or safety of human beings;


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● to any aquatic or non-aquatic organisms; ● to the resource quality; or ● to property. The main aim of the investigation discussed in this can therefore be summarized as the prioritization of the type of pollutants and their associated sources which present a threat to groundwater, the environment and health in South Africa’s urban catchments. 2 METHODOLOGY 2.1 Factors taken into account The methodology followed evaluated the sources and contaminants separately. The results of the evaluation were then combined to determine a final risk based prioritization. 2.1.1 Sources Sources, in this context, refer to the origin of the substances (inorganic species, organic compounds or microbial agents) that are causing, or may potentially cause, the pollution. The term

Table 1. Systems for classification of groundwater contamination sources. Classification Examples system based on Way of release Loading history Location Degree of localization Origin Likelihood of occurrence

Discharge sources, transport sources Spill or continuous Above ground surface, below surface Point (or line) and non-point sources Industrial sources, mining sources For example petrol service stations found more often than chemical manufacturing plants

is used very broadly over a range of scales and may describe physical entities (e.g. a pond, a tank, a pipeline); human activities (e.g. mining, irrigation, wastewater treatment); the site at which potential pollutants are stored, used or disposed (e.g. wastewater treatment works, cemeteries, fuel filling stations) or even large scale phenomena (e.g. atmospheric deposition).

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Source of pollutant plays a large role in whether the pollutant will reach the groundwater table and if it does the rate at which the pollution will enter the groundwater system. There are also several existing methods for classifying the sources of groundwater pollution. A simplified classification based on that of Nonner (2002) was used to classify South African sources (see Table 1). 2.1.2 Pollutants Pollution refers to levels of hazardous substances in the environment over and above what would ordinarily be found in the absence of local activities. Groundwater pollution therefore refers to the occurrence of substances (inorganic species, organic compounds or microbial agents) in concentrations above those that would naturally be found in an aquifer. The substances themselves, both chemical and microbial, are called pollutants. There are various ways in which to group or classify groundwater pollutants. Each of these has major classes which can then be broken down into smaller categories. The choice of system and level of detail of the classification is dictated by the purpose of the classification for the sake of this investigation pollutants were classified according to: ● Fate in the environment – Degradable pollutants, which can be rendered harmless by natural processes and need therefore cause no permanent harm if adequately dispersed or treated; and – Persistent pollutants, which eventually accumulate in the environment and may be concentrated in food chains. – Pollutants may also be divided by their behaviour in water into: (a) Soluble pollutants, which includes most inorganic species and some organics. (b) Insoluble substances, which are small enough to be carried through the aquifer matrix, including microbial pollutants and colloidal inorganic pollutants. (c) Non-aqueous phase liquids (NAPLs), which are organic compounds that do not dissolve readily in water and remain as a separate liquid phase. These are further subdivided into Light Non Aqueous Phase Liquids (LNAPLs) and Dense Non Aqueous Phase Liquids (DNAPLs). ● Human health impacts – Non-harmful substances, which have no observed effects on human health. – Toxic substances, which cause various effects on the body from short-term exposure or long term accumulation, ranging in severity depending on the dose e.g. nausea, rashes, kidney failure or neurotoxic effects. – Carcinogenic substances, which are known to cause cancer. – Pathogenic substances, which are known to cause diseases in humans. ● Other aspects that are taken into account: – Duration of pollution—if the pollution results from a single (once-off) spill, the impact will probably be smaller than that resulting from continuous pollution. – The vulnerability of the aquifer represents the intrinsic characteristics that determine the sensitivity of an aquifer to the adverse effects resulting from the imposed


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pollutant (Lynch et al., 1994). Factors taken into account include depth to groundwater, recharge, aquifer media, soil media, topography and impact of the vadose zone. 2.2 The risk-based methodology Rating occurs when contaminant sources are given a quantitative or qualitative measure of the potential hazard they pose to groundwater. Prioritisation methods focus on aspects such as contaminant loading, mobility, persistence and hazardousness while risk assessment develops these further into potential human health impacts. A risk analysis estimates the probability and consequences of a contaminant event and usually considers both the properties of the contamination source and the hydrogeological environment. Conventional set theory (Boolean) states that an element is either a member of a set or not. Fuzzy logic is an extension of conventional set theory enabling an element to belong to a set to a degree. The degree of membership is a function that defines the membership of an element to a set according to the value of the element. Membership is expressed as a value between 0 and 1. Zero implies 0% membership and 1 implies 100% membership. Linear membership functions are seldom used in practice in contradiction to sinusoidal functions which are very popular. In most cases risk analysis will involve more than one input to be considered in the analysis. Fuzzy logic makes it possible to generate a set of decision rules according to the number of inputs and these rules must then be evaluated by an expert in the field of study. The number of rules generated is given by the following equation is: n=2inputs where n represents the number of rules generated. The rules consist of all possible binary combinations of the respective inputs with a weight assigned to each rule representing the risk. The risk is then calculated using the following formula:

where n=number of rules, DOM=degree of membership and Wn=weight of rule n. 2.3 A tiered approach Based on the amount of data available a tiered approach is followed when considering risk assessments. The first tier (LEVEL 0) is a rapid assessment of sources in which minimal data are required and it produces low confidence results. This assessment should be completed within a few minutes and is based on a rating system. LEVEL 1 is the second tier which is a rapid assessment of contaminants on a local scale. It is intended to


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give the assessor a guideline of the risks. The assessment should take a couple of hours to complete. The next tier (LEVEL 2) is an intermediate assessment. The first step in the intermediate assessment is to collect all relevant data. Data requirements include aquifer and contaminant parameters, as well as health information. General information will be obtained from databases, but it is sometimes necessary to have site-specific data. The confidence attached to this assessment should be medium to high. Both the second and third tiers include risk assessments based on a fuzzy logic methodology. Figure 1 is a schematic representation of the tiers and the function performed on each level of assessment.

Figure 1. Tiered approach to South African prioritization methodology. In order to protect boreholes wellhead protection areas (WHPAs) need to be delineated. A WHPA can be defined as the surface and subsurface area surrounding a


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borehole or wellfield, through which contaminants are reasonably likely to move and reach such a borehole or well field. In many cases it is difficult to protect the whole area, therefore various zones are established within the area. 3 CASE STUDY: CAPE FLATS WASTEWATER TREATMENT WORKS 3.1 The wastewater treatment works within the City of Cape Town prioritization of sources and contaminants on a regional scale The City of Cape Town (CCT) is located in the Western Cape Province on the southeastern corner of South Africa. A major portion of the CCT consists of the area known as the Cape Flats, which has an elevation of between 20 and 45m above sea level. CCT has a mean annual rainfall of 515mm/annum and an average temperature of 16.7°C. It is a winter rainfall area. The current population of the CCT is estimated at 3.2 million with the highest population density occurring on

Table 2. Source prioritization for CCT (incomplete list). Source prioritisation (from highest to lowest risk) On-site sanitation Petrol service stations (underground storage tanks) Cemeteries Stormwater/sewer systems Agriculture (general and crop cultivation) Feedlot/poultry farms Wastewater treatment

Table 3. Contaminant prioritization for CCT. Contaminant prioritisation (from highest to lowest risk) Nitrate Chloride Phosphate Potassium Ammonia & sulphates


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Table 4. Information used in site-specific risk assessment. Parameter

Assigned value

Vulnerability –Recharge 65mm/yr –Soil media Sa-LmSa –Aquifer media Intergranular –Vadose zone Beach sand –Groundwater depth 8m –Topography 1% Duration Continuous Contaminant* Nitrate Level of management Low *Once the contaminant is entered the software automatically pulls in the health risk information and physio-chemical behaviour from a database.

the Cape Flats and there are approximately 90000 consumers on informal sites. There are 21 wastewater treatment plants within the CCT. According to TIER 0 the wastewater treatment works are rated as the 7th highest pollutant source within the CCT. Due to the length of the complete list only the 7 highest potential polluters have been documented in Table 2. Typical contaminants found at wastewater treatment works include ammonium, nitrate, potassium, phosphate, chloride, sulphate and faecal pathogens. Micro-organisms were not included in the investigations and will therefore not be included in the prioritization list. The prioritization of the above-mentioned chemicals is listed in Table 3. 3.2 The Cape Flats wastewater treatment works risk assessment The wastewater treatment works has unlined sewage sludge drying ponds. The wastewater treatment works are situated on an unconfined primary sand aquifer. The information used to determine a site-specific risk is listed in Table 4. For the sake of demonstration only the risks for nitrates will be determined in this paper. The results of the assessment are summarized in Table 5.

Table 5. Results of risk assessment. Assessment

Risk (%)*

Source 58 Vulnerability 52 Health 99 Physio-chemical 75 Total 68 * Higher the risk higher the negative impacts.


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Table 6. Data used to calculate protection zones. Parameter

Assigned value

Abstraction rate Transmissivity Effective porosity Hydraulic gradient Saturated thickness

10l/s 100m2/d 0.1 0.01 20m

Table 7. Calculated protection zone. Definition

Radius (m)

Zone 1: Highly protected area around the borehole. Its purpose is to protect the borehole from the direct introduction of pollutants into the borehole and its immediate area from spills, surface runoff, or leakage from storage facilities or containers. Potential pollutant sources in Zone 1 should be strictly monitored. 25 Zone 2: Is established to protect a borehole from contact with pathogenic micro-organisms which can emanate from a source located close to the borehole, as well as to provide emergency response time to begin active cleanup and/or implementation of contingency plans should a chemical contaminant be introduced into the aquifer near the borehole. 470 Zone 3: Is designed to protect the borehole from chemical contaminants that may migrate to the borehole; it typically includes a major portion of the 750 recharge area or the capture zone.

The results of the risk assessment for nitrates indicate there is a 68% chance that there are going to be negative impacts on the environment (including human health) as a result of groundwater becoming polluted with nitrates as a result of the wastewater treatment works. 3.3 Protection of boreholes The distance between a pollution source and a protected borehole can be calculated to ensure the borehole is not polluted. The zone of protection can then be delineated around the borehole. These wellhead protection zones can also be used to plan new boreholes. If all pollution sources are known then the ‘safe’ distance from a source can be calculated.


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Wellhead protection zones were calculated for boreholes in the Cape Flats. Table 6 contains the information needed for the calculations and Table 7 defines the protection zones and gives the radius of protection zones. 4 CONCLUSIONS AND RECOMMENDATIONS Pollution of South Africa’s urban aquifers presents a threat to the sustainability of this water resource. Man’s activities, use of chemicals and generation of wastes tend to concentrate potential sources of pollution in the urban areas. The threat caused by undesirable substances is recognized in this country, but the understanding of the extent of the problem in South Africa’s urban catchments is poor. This paper therefore briefly outlined a risk-based methodology to prioritise and determine the impacts of pollutant sources and pollutants. The methodology takes the following into account: ● Characteristics of pollutant sources ● Characteristics of pollutants ● Human health impacts of pollutants ● Vulnerability of South African aquifers ● Duration of pollution The methodology was then applied to determine: ● National list of priority chemicals and sources ● Regional list of priority chemicals and sources for the large South African urban areas ● Local risk assessments to determine the risks of certain pollutants ● Delineation of protection zones The results are intended to help groundwater practitioners and water authorities in assessing the likely transport, fate an impact of pollutants in the subsurface in an urban environment. It is recommended that the following aspects receive more attention in future research investigations: ● Based on the paucity of groundwater-related microbial data encountered in this project, the inclusion of these aspects in urban groundwater management must be regarded as a priority. ● Petroleum products, industrial thinners and mineral oils and other non-aqueous phase liquids represent a category of potential pollutants that have been largely overlooked by regulatory agencies and legislature, despite their harmful effects at small concentrations. ● A general lack of data on groundwater pollution from pesticides is evident. This is due to: (i) surface waters are the main source of water supply in the country; (ii) cost and difficulty to measure organic contaminants; (iii) private companies are often sensitive to make public data related to pollution problems. Therefore there is a need to investigate pesticides in groundwater.


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REFERENCES Lynch, S.D., Reynders, A.G. & Schulze, R.E. 1994. Preparing input data for a national-scale groundwater vulnerability map of Southern Africa. Water SA, 20(3):239–246. National Environmental Management Act. Act 107 of 1998, Pretoria, South Africa. National Water Act. Act 36 of 1998, Pretoria, South Africa. Nonner, J.C. 2002. Chapter 3: Sources of groundwater contamination. In: A. Zaporozec (ed.) Groundwater contamination inventory: A Methodological Guide.UNESCO, IHP-VI, Series on Groundwater No. 2. 23–38.

Understanding problems of low recharge and low yield in boreholes: an example from Ghana A.J.E.Cobbing & J.Davies British Geological Survey, Wallingford, Oxon, UK Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: The Afram Plains region of Ghana experiences acute seasonal water shortages during the four to five month long dry season. The long-term development of the limited groundwater resources of the region has proved to be difficult as the hydrogeology is poorly understood. Failure of boreholes is common, and there is little or no monitoring of groundwater levels. A two-year study led by the British Geological Survey, including the monitoring of borehole-drilling programmes, has led to a better understanding of the groundwater resources in the area and has provided guidelines for data collection.

1 INTRODUCTION The Afram Plains area is located in the Eastern Region of Ghana, in the Volta River basin between latitude 6°30′ and 7°30′N and longitude 1°00′W and 0°15′E (Figure 1). The area is about 4285km2 in extent, and lies between lake water level at 76m and 300m above mean sea level. The topography is subdued, with the main feature being a low northeast to southwest trending ridge 200–300m high. The Afram Plains supports savannah vegetation that is being progressively cleared for agricultural use. Coarse tussock-grass with a few stunted trees covers the low-lying lakeside plain and dense bush with large trees covers the better-drained ridge area. Since initial settlement in 1930, the rural population of the Afram Plains has increased rapidly following the construction of the Akosombo Dam in the 1960s. Between 1970 and 1984 census data show a 250% increase in the farming population, attracted by fertile soils and improving infrastructure. There are now more than 140 villages on the Afram Plains. Access to the area is poor, with the principal route by ferry across Lake Volta. The main town is Donkorkrom, which has a hospital, secondary school and post office.


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Figure 1. Map of Ghana showing the Afram Plains study area. 2 THE WATER SUPPLY PROBLEM IN THE AFRAM PLAINS Before construction of the Akosombo Dam, village water supplies were obtained from the perennial Afram and Volta Rivers, seasonal flows and pools along ephemeral tributary streams and shallow water-filled dugouts. Rainfall on the Afram Plains is seasonal, with an average of about 1200mm/year falling almost entirely between April and October. Surface drainage is mainly ephemeral, storm water draining by sheet flow as short-lived floods. The seasonal rainfall and limited surface water storage result in acute water shortages during the November to March dry season. Reliance on unprotected pools and dugouts for water supply results in water-washed and diarrhoeal disease, and much time and effort in water collection. Guinea worm infections occasionally occur in the Afram Plains. 2.1 Regional geology The Afram Plains are located at the southern end of the large (>100,000km2) Voltaian Sedimentary Basin formed during the Precambrian to early Palaeozoic Pan-African Orogeny of 730–550Ma. (Black and Liegeois, 1993, and Shackleton, 1976). The Voltaian Basin is interpreted as a foreland basin; with sediments of marine and terrestrial origin filling a flexural depression at the margin of the West African Craton (Ako and Wellman, 1985). Kesse (1988) and Anani (1999) describe the Voltaian basin sediments as fairly flat bedded sandstones, shales, pebble beds, mudstones, limestones and siltstones deposited unconformably upon older Precambrian rocks. The molasse type sediment pile, that is estimated to be more than 4km thick, resulted from erosion of mountain chain fold belts that occurred along the present Ghana-Togo border to the east. The Voltaian Formation

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Obosum Beds that underlie much of the southern Afram Plains have yet to be studied in detail. Present geological knowledge has been derived from rapid reconnaissance surveys, several deep exploration boreholes and a number of shallow groundwater boreholes. 2.2 Previous groundwater development Development of the groundwater resources of the Voltaian sediments of the area began in 1963–65 when the Geological Survey of Ghana and the Volta River Authority (VRA) drilled a series of test and production boreholes in response to populations displaced by the rising lake waters. During the late 1960s and early 1970s the Catholic Church funded the construction of 28 hand-dug wells to supply small villages. These were mainly located in valley sites to replace unprotected shallow dugout sources. Additional boreholes were installed by the VRA at Donkorkrom and Kaklakoklope in 1983/84. UNICEF provided a borehole for the secondary school at Donkorkrom in 1983. During 1984, Prakla Seismos drilled 47 village boreholes for the German NGO Misereor. Of these, 19 boreholes were dry and 17 had yields greater than 301min−1. Although Lake Volta forms the eastern boundary of the area, the underlying low permeability rocks are the main source of water especially in the more remote western area. During the 1990s, more than 300 boreholes were drilled to meet the water supply needs of the expanding population.

Table 1. Summary of borehole drilling on the Afram Plains, 1963 to 2001. Organisation

Period No. Wet Dry of Bhs Bhs Bhs

Volta River Authority Prakla Seismos for Misereor World Vision International World Vision International WaterAid/Afram Plains Dev. Org. DANIDA exploration boreholes Totals

1963– 1965 1984

10

6

4

47

28

19

1990– 1995 1999– 2000 1996– 2001 2001

152

92

60

66

?

?

101

67

34

5

5

0

381

198 117

Many of the boreholes drilled were dry whilst other nominally successful boreholes showed a progressive decline in yield to fail after two to three years of use, especially in the west of the area. Due to their short period of land tenure, communities have yet to develop coping strategies to manage the limited water available during dry periods.


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Populations attracted to the area by the groundwater supply have no effective alternative water source if borehole yields fail after several years of use. 3 RECENT WORK ON THE AFRAM PLAINS The British Geological Survey (BGS) first worked on the hydrogeology of the Afram Plains in 1985–86, in a project examining shallow wells and boreholes in the Donkorkrom area (Buckley, 1986). Beginning with a visit to the area in February 2000, the BGS collaborated with the Afram Plains Development Organisation (APDO), WaterAid, DANIDA, Legon University (Accra) and other partners in a two-year project specifically aimed at investigating the hydrogeological problems of the area. The BGS work was funded by the British Department for International Development (DfID). The project was timed to coincide with the drilling of 36 village water supply boreholes on the Afram Plains, funded by WaterAid working with the APDO. In addition, DANIDA funded the drilling of a further 5 deep (>100m) exploration boreholes, the first four of which were sited and geologically logged by BGS hydrogeologists. Studies carried out by the BGS in collaboration with local partners included: ● A reconnaissance geological and hydrogeological survey, and the creation of a GIS base map of the area. ● The geophysical survey of four of the five deep exploration borehole sites using frequency domain electromagnetic induction (EM34). ● The geological logging of rock chip samples produced during drilling, and the recording of penetration rates and drill stem yields. ● The test pumping of boreholes, including the demonstration of bailer tests and low yield “whale” pumps. ● The sampling of groundwaters for hydrochemical analysis of major and minor ions, and isotopes. ● The geophysical logging of the deep exploration boreholes was carried out by DANIDA.

4 SURFACE GEOPHYSICS ON THE AFRAM PLAINS Electrical resistivity and EM geophysical exploration surveys have been undertaken in the Afram Plains during other development projects. As in other hydrogeologically “difficult” areas in Africa, these methods have fallen out of favour in the Afram Plains, being seen as relatively expensive and time consuming for little benefit. This is due to a combination of: ● the mode of groundwater occurrence in the area, such as deep fractures, often thick weathered zones, that cannot be defined using geophysical surveys, ● the lack of experienced personnel capable of interpreting geophysical results for sedimentary environments.


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BGS undertook 11km of EM34 surveys at the first four exploration borehole sites, using 10m, 20m and 40m inter-coil separations. Readings were made in both vertical and horizontal orientations. The survey results were correlated with the geological logs from the exploration boreholes. Geophysicists from the University of Ghana, Legon, undertook max-min EM and electrical resistivity geophysical traverses along the main road in the eastern Afram Plains (Banoeng-Yakubo and Armah, 2001). The result of these studies demonstrate that geophysical surveys can be used in the eastern Afram Plains to differentiate between near surface shale, siltstone, sandstone and conglomerate bands, as well as delineate possible fault zones. In the west of the area, re-cemented sandstones up to 60m thick form a low permeability homogeneous layer below an ancient weathered surface. Thin water bearing fracture or weathered zones beneath this layer cannot be detected using EM34 or VES equipment. 5 DATA GATHERED DURING BOREHOLE DRILLING Useful geological and hydrogeological data that can be gathered during the drilling of a borehole includes: ● Geological data ● Penetration rate data ● Flow data ● Hydrogeological data Rock chip samples produced during drilling were collected at 1m intervals. Weathered zones (colour changes) and fracture zones (calcite and quartz mineralisation) enabled identification of water bearing zones. The chip samples were placed in a marked half pipe and photographed to produce pseudo-core logs. This procedure allowed zones of water inflow to be correlated with changes in lithology, and deductions regarding the nature of groundwater occurrence to be made. The rate of drill penetration and flow rate, determined at water strike zones and at the end of each drilling rod can be correlated with changes in lithology and weathered zones. Photo logs can show the nature of the weathered zones. The results obtained from exploration borehole showed that the rock types present are generally tight and fine-grained, with water being produced from horizontal weathered zones and along lithological boundaries rather than near-vertical fractures. In the western half of the area, the presence of a thick duricrust weathered zone, stopping recharge to underlying aquifer systems, was recognised. 6 BOREHOLE GEOPHYSICS A suite of geophysical logs was obtained from six boreholes in the study area, i.e. the five deep exploration boreholes together with a water supply borehole located at the APDO office in Tease. The calliper logs show the fracture zones, which can be correlated with the drillers report and the chip sample logs. The fracture zones are also indicated by lower resistivity measurements.


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Pumped fluid logging of the boreholes clearly shows that fluid inflows occur at discrete fractured or weathered horizons, and that most of the water obtained from the boreholes is derived from these features. The discontinuous nature of the fracture systems that supply water is illustrated by drilling at the APDO office in Tease: in 2000, a 70m deep borehole (“hole no. 28”) was drilled in an attempt to provide a water supply for the office. This borehole proved to be dry and was backfilled. In 2001 a further two boreholes were drilled within 20m of this hole, one to 54m and a deep exploration borehole to 152.8m. Both of these boreholes yielded water. 7 TEST PUMPING OF BOREHOLES Pumping test data in fractured aquifers is more difficult to interpret compared with intergranular systems. There is often a distinct change between early and late time drawdown rates, due to the effect of fracture dewatering. This can allow erroneous interpretations to be made, particularly if pumping tests are carried out over only short periods of time. Pumping test interpretation requires specific training, and pumping tests have sometimes been done on the Afram Plains merely as required by the contract, without the pumping test information being used to inform the borehole completion. BGS developed a simple bail test, which allows field personnel on the Afram Plains to decide in a general way whether or not to equip a borehole, without going through the lengthier and more complex process of a pumping test (Davies and Cobbing, 2002). There are cases however where the bail test is inconclusive and the borehole requires a pumping test. Bail tests are


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Figure 2. Geophysical logs of deep exploration boreholes at Gazeri Camp (left) and Samanhyia, near Tease. Fractured and weathered zones can be seen on the calliper and induction resistivity logs, and the pumped flowmeter logs show that most flow into the boreholes is derived from these horizons. recommended as a rapid and simple field procedure to be used by staff not trained in pumping test interpretation to decide whether or not to equip a borehole with a pump. Simple pumping tests give indications of the productiveness of the systems but the results obtained are from “fractured” aquifer systems with high secondary permeability zones are difficult to reconcile. Such systems can initially give high yields but when they are dewatered during extended periods of over-pumping these systems can suddenly fail. 8 HYDROCHEMISTRY RESULTS Water samples for hydrochemical analysis were obtained from 29 boreholes and wells during the 2001 visit. Samples were taken from sources after several minutes of pumping where possible. Measurements of pH, specific electrical conductance (SEC), temperature and bicarbonate were taken at each site. Filtered acidified and non-acidified samples were obtained from each source for laboratory analysis. A GPS was used to locate the areal co-


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ordinates of each sample site. Stable isotope analysis (δ2H and δ18O) was carried out on twelve samples by mass spectrometry. The results of these determinations plot close to the world meteoric water line. There is some evidence for the possible mixing of lakederived waters with aquifer waters in some areas. The major and minor ion analyses show that most determinants are within World Health Organisation (WHO) Guide Values, with the exceptions of boron and sodium that are a problem in the unfractured shale and sandstone area. Nitrate and ammonium levels in a few boreholes were evidence for anthropogenic pollution, which can occur because water is able to move relatively rapidly through fractures. The fluoride concentration in one sample exceeded WHO Guide Values. 9 HYDROGEOLOGY OF THE AFRAM PLAINS A five-fold hydrogeological division of the rocks of the Afram Plains can be produced, based on the conclusions of Bannerman (1990) and Acheampong (1996), and taking the current study into

Figure 3. Five hydrogeological divisions on the Afram Plains. account (Figure 3). The hydrogeology of each of these units is summarised in Table 2. 1. Massive conglomerate and sandstone. 2. Fractured shale and grey sandstone. 3. Quartzitic sandstone and conglomerate.


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4. Feldspathic sandstone, arkose, siltstone and mudstone. 5. Unfractured shale and sandstone.

10 DISCUSSION In regions of seasonal or low rainfall with ephemeral drainage patterns rural settlements may be totally dependent upon groundwater supply during the dry part of the year. Such is the present and future shortage of land in many areas that communities once settled in water poor areas are difficult to move. Therefore understanding of groundwater resources is a vital factor for long-term development plans of such marginal areas. Groundwater development in the Afram Plains has followed a pattern that is typical of areas underlain by low permeability rocks in sub-Saharan Africa. Reconnaissance level geological and hydrogeological surveys were first undertaken with limited drilling more than thirty years ago. Some borehole drilling by the VRA was undertaken at the time of population resettlement following the building of the Akosombo Dam and consequent flooding in the 1960s, but these boreholes have fallen into disuse following lack of maintenance. NGO-led water supply programmes, undertaken by World Vision International, a Catholic Church Group and WaterAid, funded the drilling of some 370 boreholes on the Afram Plains during 1984–2001. During these programmes the economic design and construction of boreholes, and borehole drilling “success rates” were emphasised. A borehole was judged a success if “wet” at the completion of drilling. The hand pump equipped boreholes were expected to supply 250 people with at least 20 litres per capita of water per day. In the Afram Plains the acceptable yield minimum is about 121min−1, due to the low borehole yields obtained. The high borehole “failure rate” (40%) has led to further study of the distribution of fracture and near surface weathered zones, these being perceived as the best groundwater bearing targets. Although many boreholes have been drilled, the geology of the area, groundwater occurrence, and the nature of the water resource remain poorly understood. This problem is exacerbated by the failure of apparently successful boreholes after 3–4 years of use.

Table 2. Summary of the hydrogeology of the five hydrogeological units. Description Ground of rock/ water hydrogeology targets unit Obosum Massive Beds— conglomerate Upper and sandstone Voltaian System

Ground Ground Field Technology Comments water water techniques potential quality

Weathered ** zones and fracture zones. Success rate ~66% wet 38%≥30l/min

Good. Presence of NO3N and NH4 indicates pollution in heavily used

Weathered Boreholes conglomerate 60–100m gravel often visible at surface: EM34—used to locate fractures and sandstones/ conglomerate

Good recharge, best sites located in valleys. Boreholes should be drilled to below present day


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boreholes near surface. in village VES— centre. indicates depth of weathering

Quartzitic Weathered ** sandstone and zones and conglomerate fracture zones. Success rate ~67% wet 40%≥30l/min

Good.

Quartzitic Boreholes sands often 100–150m visible at surface. EM34—used to locate fractures and sandstones/ conglomerate near surface. VES— indicates depth of weathering

Feldspathic sandstone, arkose, siltstone and mudstone

Good.

Weathered Boreholes purple brown 100–150m sandstone platform surface beneath thin ferrecrete. Difficult to identify fractures with EM34, sandstones have been recemented to 60 m. VES—may indicate

Weathered */** zones and fracture zones. Success rate ~66% wet 39%≥30l/min

lake level. May be able to induce flow from the lake along fracture zones, Problems with pollution in villages. Moderate recharge, best sites located in valleys. Boreholes should be drilled to below present day lake level. May be able to induce flow from the lake along fracture zones. Problems with pollution in villages. Very poor recharge potential due to recemented layer down to ~60m. Deep holes may intercept weathered zones, Remoteness precludes direct recharge from lake


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depth of weathering

along fractures, Fractures poorly defined.

Description Groundwater Groundwater Groundwater Field of rock/ targets potential quality techniques hydrogeology unit

Technology Comments

Unfractured Weathered * shale and grey zones and sandstone fracture zones. Success rate ~50% wet 14%≥30l/min

Poor to saline. Low lying Boreholes— low altitude 50–100m lake side areas. EM34— moderate to high conductivities, used to locate fracture zones VES— indicates depth of weathering

Fractured shale Weathered *? and sandstone zones and fracture zones. Success rate Unknown due to lack of data

Poor to saline?

Poor to moderate recharge to tight formation except where conglomeratic bands area present. Boreholes should be drilled to below present day lake level. Boreholes— Unknown 50–100m

Low lying low altitude lakeside areas. EM34— moderate to high conductivities, used to locate fracture zones VES— indicates depth of weathering

KEY: Groundwater potential: *Low; **Moderate; ***High. Note: Groundwater Potential is an overall function of groundwater storage, groundwater yield and groundwater residence time (length of time groundwater remains in the unit, i.e. rate of groundwater throughflow). It indicates both the available yields and the length of time these are available for: i.e. high, moderate or low yields, available only during the wet season and immediately afterwards, or yearround. See below for more detail. EM34 conductivity response: High>50mmhos/m; Moderate 20– 50mmhos/m; Low 1l/s; Moderate ~0.5l/s; Low 0, Rf120MMA−ThF) The calibrated parameters for the system have been determined as ReN (7%), ReF%(44), ThN(26mm) which the recharge threshold and ThF(43mm) which is the flood recharge threshold. The Rf values all refer to the month lag included. The equation therefore amounts to Equation 5: Schoonspruit Flow (Mm3/m)=(0.07*Rf24MMA/Rf120MMA*(Rf96MMA−26)*0.842) (5) +(0.44*(IF((Rf120MMA−43)>0, Rf120MMA−43))*0.842)−AbsGW This equation is used in the groundwater management tool of the Schoonspruit dolomitic compartment. The biggest advantage of this method is that abstractions can now be incorporated into the simulation and predictions can be made with long-term predicted rainfall. The effective recharge for the Schoonspruit Eye was determined as 13% for 2002.


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4 MANAGEMENT TOOL 4.1 A first order groundwater management tool The basic principle of a first order tool is to include the essential mechanisms in an understandable format, which will be used by the most basic groundwater manager. Inputs into the tool must be simple and outputs easily usable, while a layman should not change the driving equations. When new information becomes available, the tool should be easily modified by professionals, to include refined parameters or simulations. Developing a groundwater management tool is dependent upon the geotechnical controls essential to the management of the dolomitic compartment and which are only beneficial. Therefore the tool cannot be developed before the geohydrological evaluation has been complete and all essential controls have been defined and determined. Essential outputs from the tool include groundwater balances for various zones in the compartment, annual recharge volumes and therefore allocable volumes in the compartment, spring flow simulations for predictions from rainfall, including allocable volumes for both groundwater and surface water users and a classification of the groundwater quality based on the standards for the use of the water on the compartment. Beneficial outputs from the tool include a warning system if the Resource Quality Objectives are not met and the management class of the aquifer incorporated into the allocable volumes. 4.2 Users The users of such a tool range from the groundwater user’s association to the regulators and also groundwater consultants operating in the area. The tool needs to be versatile and contain all the necessary geohydrological equations, yet at the same time to be userfriendly. Equations for inclusion in this tool included the Schoonspruit Eye simulation equation and incorporation of domestic and ecological requirements. 4.3 Input The tool was constructed in such a way that only the latest rainfall and water quality need to be included as time-variant data. Aspects such as the reserve requirements and rainfall/recharge equations are built in. 4.4 User-friendly tool The management tool was programmed with macros which guide the user, in MS Excel. The Title page of the Tool is an information page only and a navigational button move to the next sheet, the Menu sheet. The “Enter Data” button navigates to the Data sheet, the “Compartment Map” button to the Map sheet and the “Assign/check Volumes” button to the Volume sheet. This is a navigational sheet only and the pathways are inserted here is up to the developer. The Data sheet of the Tool, allows input of the groundwater

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quantities and qualities. Data input includes compulsory data inputs and optional data inputs. The optional data are helpful if available, but the simulations are not dependent on these cells to run. Navigational buttons to other sheets and data entry points are also included. The Drinking Water Quality Classes for the different parameters are included as fixed parameters. On the Prediction sheet of the Tool all the calculations for the simulation of the Schoonspruit Eye flow, therefore allocable volumes are done. The simulated flow (Mm3/m) is then determined using the spring flow equation as only rainfall values, and not equations, are now incorporated. Input data to this sheet is obtained from the Data sheet. Allocable volumes are determined with the simple equation of subtracting surface water demand from the simulated flow, as this has already taken into account current groundwater use. Figure 4 shows the spring flow and allocable volume graph. 5 DISCUSSION The aim of the groundwater management tool was to provide a first order technical tool, which is a practical and workable tool, for use by the WUA in determining allocable volumes. The following conclusions are made with regard to the groundwater management tool: ● Input and output parameters as outlined in this paper were used and proved to be sufficient for defining quantity and quality concerns in the Schoonspruit dolomitic compartment. ● Allocable volumes can be determined for the two zones using predicative rainfall data. ● The Schoonspruit Eye can be simulated using predicative rainfall data with the following equation:

Schoonspruit Flow (Mm /m)=(0.07*Rf24MMA/Rf120MMA*(Rf96MMA−26)*0.842) +(0.44*(IF((Rf120MMA−43)>0, Rf120MMA−43))*0.842)−AbsGW 3


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Figure 4. Spring flow and allocable volume graph of the SGM tool. ● The drinking water quality classes were introduced, as a useful parameter, as part of an early warning system where drinking water quality is of concern. ● The tool is sufficient to continue with groundwater management in the dolomitic compartment. ● Verification of the lawful users is of utmost importance for groundwater management to be successful. ● The tool is a practical and useable tool for all groundwater managers and planners. The following recommendations are made with regard to the groundwater management tool: ● Groundwater management should commence at once and the tool tested against annual data. ● Verification of lawful water uses should continue and be completed as soon as possible. ● The tool should be tested and applied to other dolomitic areas.

REFERENCES Bredenkamp, D.B., Botha, L.J., Van Tonder, G.J. & Van Rensburg, H.J. 1995. Manual on quantitative estimation of groundwater recharge and aquifer storativity. Report no. TT 73/95. Water Research Commission, Pretoria. Bredenkamp, D.B. & Swartz, A. 1987. Reconstruction of the flow of springs by means of annual recharge estimates. Technical report no. GH 3525. Department of Water Affairs, Directorate Hydrology, Pretoria. DARCY Groundwater Scientists and Consultants. 2002. A catchment management plan for the Schoonspruit and Koekemoer Spruit catchments: A groundwater situation analysis. Department of Water Affairs & Forestry, Bloemfontein.

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Fleisher, J.N.E. 1981. The geohydrology of the dolomite aquifers of the Malmani Subgroup in the SouthWestern Transvaal, Republic of South Africa. Technical report no. GH 3169. Department Water Affairs & Forestry, Directorate Hydrology, Pretoria. Kok, T.S. 1972. Wes-Transvaal en Noord-Kaap waterbeplanningstreek—geologie, fonteine en myne in opvanggebied. Technical report no. GH 1758. Department of Mines, Geological Survey, Pretoria. Kotze, J.C. 1994. Summary of the Geology, Geohydrology, and Boundaries of the proposed SGWCA, District Ventersdorp, Drainage Area C24. Technical report no. 3833. Department of Water Affairs & Forestry, Directorate Hydrology, Pretoria. National Water Act, Act No. 36 of 1998. Polivka, J. 1987. Geohydrological investigation of the Schoonspruit compartment in the dolomitic area of Ventersdorp. Technical report no. GH 3524. Department of Water Affairs, Directorate Hydrology, Pretoria. Schoeman & Vennote. 1996. Ventersdorp Oog Ondergrondse Staatswaterbeheergebied. Report no. B0307/2. Department of Water Affairs & Forestry, Sub directorate Water Allocation, Pretoria. Selaolo, E.T. 1998. Tracer Studies and Groundwater Recharge Assessment in the Eastern Fringe of the Botswana Kalahari. Ph.D. thesis, Free University of Amsterdam. GRES Project Publication. Van Tonder, G. & Xu, Y. 2001. A guide for the estimation of groundwater recharge in South Africa. The Institute of Groundwater Studies, Bloemfontein. Vegter, J.R. 2001. Groundwater development in South Africa and an introduction to the Hydrogeology of groundwater regions. Report no. TT 134/00. The Water Research Commission, Pretoria. Veltman, S. 2003. A Methodology for Groundwater Management in Dolomitic Terrains with the Schoonspruit Compartment as Pilot Area. Unpublished M.Sc thesis. University of the Free State, Bloemfontein, South Africa.

Effects of mining and urban expansion on groundwater quality in Francistown, Botswana Benjamin Mafa Department of Water Affairs, Gaborone, Botswana Horst Vogel Department of Geological Survey, Lobatse, Botswana Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: This study was carried out as part of a technical cooperation project between the Department of Geological Survey in Lobatse and the German Federal Institute for Geosciences and Natural Resources. The aim was to determine if groundwater pollution had taken place in Francistown (NE Botswana) due to urban expansion and/or historic gold mining activities, and to delineate affected areas as well as potential groundwater hazards on thematic maps which were designed in a digital and easily readable form for future development planning by urban planners. The results revealed that groundwater in Francistown had indeed become polluted through pit latrines, gold mine tailings dumps, and waste disposal sites (landfills). Different pollutants were associated with specific pollution zones. Groundwater from boreholes located within these zones was not suitable for human consumption because it exceeded certain World Health Organization and Botswana Bureau of Standards recommendations for drinking water. The study revealed that groundwater pollution due to nitrates constitutes a real health hazard and environmental and health hazards emanating from abandoned mines jeopardized human safety and environmental protection and was obvious from observed chemical “cocktail” conditions of tailings dumps and trace element concentrations in some boreholes.

1 INTRODUCTION Francistown is the oldest established town in Botswana. Born during the late 19th century as a gold mining town at the confluence of the ephemeral Tati and Ntshe sand rivers,

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Francistown is the commercial hub in the NE of Botswana. The city’s rapid economic development, in particular since the 1970s, has caused its population to triple over the last three decades to approximately 100,000 inhabitants. Today Francistown is the second largest city in Botswana. In the not too distant past, water demands were entirely met by groundwater locally available from shallow alluvial and fractured volcanic rock aquifers. However, in the 1970s it was found that groundwater produced from the city’s public wells contained elevated concentrations of nitrate. In addition, the available limited groundwater resources could no longer meet the steadily rising demand for water. For these reasons public water supply was shifted in 1982 to surface water from the Shashe dam, which is located at a distance of approximately 30km to the SW of Francistown. The Shashe dam was built during the 1970s to supply the copper-nickel mine in Selebi-Phikwe. 2 GEOLOGY The prevailing dendritic drainage pattern consists of a system of irregularly branching tributaries and forms junctions at various acute angles. This is a manifestation of the complex folded and contorted metamorphosed rocks where lithological variations (in terms of weathering and erosion) are insufficient to modify this pattern. A significant portion of the Francistown study area consists of rocks of the basement complex including meta-volcanics of the so-called Tati schist group. The basement complex is divided into various granitic formations and two non-granitic lithostratigraphic units (Gibb & Partners, 1987). These are subdivided into three formations, the first of which is correlated with the Lady Mary volcanic formation. This formation consists of a homogeneous succession of dark coloured, fine-grained amphibolitic schists. The Lady Mary formation is overlain by the Penhalonga formation, which includes both metasediments and meta-volcanics. The latter are predominantly meta-andesite (greenstone) lavas, tuffs and agglomerates with amphibolite and meta-tuff beds (Key, 1976). The Selkirk formation at the top of the schist relic is laterally more restricted than the other two formations and consists of mainly felsic meta-volcanic extrusives with minor intercalations of meta-sedimentary schists. Gold mineralization in the Francistown area is mainly from quartz reefs and fissure veins of the Tati schist relic. Indeed the Tati schist relic has also been recognized for its base metal potential. Copper and nickel deposits have been identified and are now mined at the Selkirk and Phoenix mines near Matsiloje, 40km further to the SE of Francistown. Copper-zinc anomalies have also been reported near the contact between the Penhalonga and Lady Mary formations as well as in several ironstones in these formations. 3 HYDROGEOLOGY Very little detailed groundwater monitoring of the Francistown aquifers was undertaken since the first abstractions in the early 1950s and since the recommendations made by


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consultants in 1974 (Colquhoun et al., 1974) and in 1979 respectively (Gibb & Partners, 1987). Groundwater consultants identified the major aquifer in Francistown as the Penhalonga mixed formation about 1.5km wide extending for at least 7km downstream of the Tati and Ntshe river confluence (Colquhoun et al., 1974). The most productive aquifers were recognized as relatively shallow discontinuous zones of fracturing. These fracture zones have a high transmissivity and draw from storage in the overlying weathered rock and alluvium. They may be up to 4m thick and are usually semi-confined by alluvial sediments and clayey weathered rock. Confining layers composed of sandy horizons contain water and contribute leakage into the underlying aquifer thereby acting as perched aquifers. Weathering appears to be confined to certain horizons within the Penhalonga mixed formation where it appears to be restricted to the easily weathered acid meta-volcanics. Indeed the river Tati is an excellent outward expression of this feature since it also follows the geological strike of this formation within these acid metavolcanics. The river tends to change its course where it traverses more competent members of the Penhalonga mixed formation. Groundwater also occurs in the sandy channels of the rivers Tati and Ntshe and this perennial baseflow component may also be regarded as an aquifer. Upstream of the confluence, the river Tati is 35 to 40m wide with the average thickness of the sand bed being 1.7m. However, sand pockets of up to 3m deep exist and increase the saturated storage of this aquifer. Downstream of this confluence, larger volumes of water can be stored since the river becomes wider with widths ranging from 20 to 100m and deeper sand beds of more than 2m in parts. 4 METHODS AND MATERIALS The study commenced with a census of all existing wells so as to establish their distribution, usage, and availability for sampling. A Garmin 40 hand-held GPS (http://www.garmin.com/) was used for coordinate acquisition. Similarly, all industries and other sites that may have a negative impact on groundwater quality were mapped. Boreholes that were found to be accessible in terms of water level measurement were used together with the topographical elevation to infer groundwater flow directions. An electrical dipper was used for water level measurements and a Trimble high-precision GPS for ground elevation measurements as well as more accurate Cartesian coordinates. The sampling of accessible boreholes involved the use of a Grundfos MP1 submersible pump (http://www.grundfos.com/) equipped with riser pipes of up to 90m. All discharge water generated while pumping was released at least 30m away from the borehole down gradient of the prevailing land slope. The method of sampling was such that electrical conductivity and groundwater reaction were measured continuously until both parameters had stabilized. Once they had stabilized a groundwater sample was taken from the particular borehole. The sample bottles were all made of plastic. Upon sampling, water reaction (pH), electrical conductivity (EC), and dissolved oxygen (DO) were measured using hand-held meters (http://www.wtw.com/). Bicarbonate determined through titration.

and carbon dioxide (CO2) were


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The data obtained from the various fieldwork exercises and the hydro-chemical laboratory analyses were used to produce several environmental geology maps. For this to materialize, all data were transferred to the ArcView GIS software (Version 3.2) environment (http://www.esri.com/) where the various data layers were put together to produce the thematic maps. Data obtained from the chemical analyses were also used to deduce redox conditions, to delineate redox zones, and to determine the predominant redox processes. 5 RESULTS Out of the total of 202 boreholes that were identified during the well census, only 48 could be sampled for groundwater. All the others were inaccessible because of collapse, vandalism, or else, they had fallen dry. The vast majority of the accessible boreholes were concentrated along the two rivers Ntshe and Tati. However, groundwater yields were generally low. Several of the few known borehole yields were below 2m3/h, hence their proximity to the rivers. Only very few such as the monitoring boreholes at the abandoned and the new waste disposal site were beyond the rivers. The chemical analyses revealed that there was not much variation in groundwater reaction (pH). Most of the samples had neutral pH levels around 7, which is normal for groundwater. No groundwater sample showed acid conditions. Magnesium (Mg2+), calcium (Ca2+), and bicarbonate were the most important ions. Hence, Mg-Ca-HCO3 type of water was dominant. In some places, NaMg-Ca-HCO3 type of waters were prevalent that also featured elevated concentrations of , chlorine (Cl¯), and sulfate The concentration of total dissolved nitrate solids (TDS) was less than 1000mg/L in these particular boreholes. Over most of the built-up city area the groundwater was strongly influenced by anthropogenic activities. This was evident from TDS levels greater than 1000mg/L, and and constituted the dominant anions. In order to identify and delineate Cl¯, distinct groundwater pollution zones, all chemical groundwater parameters were used as environmental indicators and mapped individually. The concentration of oxygen allowed to identify zones with different aeration status, namely zones with aerobic (oxic) and those with anaerobic (probably reduced) groundwater conditions. This was the starting point towards defining likely pollution zones and also towards predicting redox states. In order to allow for a sound investigation it was necessary to examine the main indicator species for redox state, namely sulphate

ferrous iron (Fe2+),

nitrite and ammonium . manganous manganese (Mn2+), nitrate As was to be expected, a comparison between these species revealed that areas with high and . Equally, levels of Fe2+ and Mn2+ had at the same time low levels of areas rich in sulphates and nitrates coincided with zones high in dissolved oxygen (O2), indicating oxidizing (aerobic) conditions, while zones high in ferrous iron and


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manganous manganese overlapped with zones very low in dissolved oxygen, thus indicating reduced (anaerobic) environments. The change from one zone to another was gradual. Important information in order to identify buffering systems was the presence of carbon dioxide (CO2) and bicarbonate . The distribution of these two species did not show a significant relationship to the redox state of the water. It rather was related to the calcium (Ca) and magnesium (Mg) distribution. The next parameter under consideration was the distribution of chloride (Cl¯). Due to its significant mobility, Cl¯ was meant to point to possible pollution sources. Yet, only few zones of high concentration could be identified. The next step was to seek out possible pollutants, that is heavy metals and other trace elements. All heavy metals that were detected in the study area showed distributions quite different from each other and were possibly related to mine waste sites. Zinc (Zn2+) however was not connected to mine dumps only; very strong concentrations of reduced Zn were much wider spread. The spatial distribution of the different pollutants revealed that they formed zones. Thus, once the areas with oxic (aerobic) and anoxic (anaerobic) groundwater environments and the spatial distribution of pollutants were identified, the study area could be divided into different pollution zones (Fig. 1):


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Figure 1. Groundwater pollution zones in Francistown in the year 2000. Zone I—Oxidizing conditions, lots of dissolved oxygen, lots of nitrate, sulphate present, very low concentrations of ferrous iron and manganous manganese; mostly organic pollution. Zone Ia—A local disturbance within Zone I showing presence of trace elements. A small mine dump was next to this site. Zone II—High concentrations of ferrous iron and manganous manganese, enhanced zinc, no sulphate, no nitrate, ammonia present indicating very reduced conditions possibly due to organic pollution but also danger from precipitation of sulphides of different metals.


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Zone III—Typical mining waste point. Elevated heavy metal and trace element concentrations, very high arsenic concentration, but also high nitrate and sulphate levels. Ferrous iron and manganous manganese strongly decreased. Zone IV—Reduced zone with high Zn2+ and Cr concentrations; Fe2+ and Mn2+ enhanced. Some trace elements present. Zone IVa—Disturbance within Zone IV with high oxygen concentration and some elevated heavy metals and trace elements; Cl¯ also highly concentrated. Zone V—Oxidised, very high sulphate and chloride concentrations; no nitrate; trace elements in significant concentrations; some heavy metals present; controlled landfill. Zone VI—Reduced, but no Fe2+ and Mn2+; Cl¯ highly concentrated; Mg2+ and Ca2+ ; some trace elements present; old and abandoned enhanced as well as CO2 and landfill. Zone VII—Oxidising conditions; no organic pollution but very diverse trace elements present (some of them concentrated); no potential source of pollution could be identified from the groundwater hazards map. 6 DISCUSSION The results of this study revealed that groundwater in Francistown had become polluted through three major sources, namely pit latrines (Zones I and II), mine tailings dumps (Zones Ia, III, IV, IVa, and VII), and waste disposal sites (Zones V and VI). 6.1 Pit latrines—Zones I and II Chemical analyses showed that nitrate concentrations (Fig. 2) well above the Botswana drinking water standard of 45mg/L (BOS, 2000) were frequent within the city area, that is zones I and II. The areas where the boreholes revealed elevated nitrate levels matched well with the areas where pit latrines where to be found. Pit latrines were located all along the river Tati throughout the built-up area. They constitute a constant source of organic pollution in the form of human excrements. This problem is made worse by the fact that pit latrines are also being used to discharge household wastewater. It is likely that a considerable amount of pollution may have been transferred into zone I from the reduced zones IV and VII upstream to the north. Zone I was characterised by a high concentration of dissolved oxygen. Nitrogen originating upstream as well as from zone I itself was probably oxidized to nitrate, which showed an extremely high concentration in the centre of the zone. Downstream the concentration of dissolved oxygen decreased. At the same time the nitrite concentration increased, probably due to denitrification. The high nitrate concentrations gradually decreased towards zone II. In contrast, the concentrations of Fe2+ and Mn2+ were very low in the centre of zone I and gradually increased towards the reducing zone II. This was typical of a redox state controlled by bacterial activity. In zone I there was a lot of organic matter input, which may have been used by bacteria as a source of carbon for the oxidation of Fe2+ (cf. Christensen et al., 1995). In the southern part of Francistown, the river Tati flows in south-easterly direction and then bends back towards the west in the middle of zone II (cf. Fig. 1). Between the two


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bends ephemeral river flows are slowed down and the observed depth to the groundwater was shallower here than elsewhere in Francistown. In the crest of the second river bend there were big alluvial

Figure 2. Nitrate concentrations (mg/L) in Francistown in July/August 2000. deposits, which probably resulted in the accumulation of organic pollution and reduced groundwater conditions. At this point was hardly measurable but showed strong concentration. Fe2+ and Mn2+ were also strongly concentrated along with Zn2+. This was indicative of strong anaerobic bacterial reduction processes. On the edge of zone II towards zone III there was an old sewage pond. This location could be picked up in the form of a prolonged reduced zone characterized by lower and very high Mn2+ levels. Surprisingly though, the concentration of Fe2+ was low. From this it appeared that Mn reduction was somehow favoured over Fe reduction, which may have been controlled by the redox state of the pond (Mn needs less energy for oxidation than Fe). 6.2 Mine waste dumps—Zones Ia, III, IV, IVa, and VII Several groundwater zones were indicative of pollution due to historic gold mining activities. The strongest evidence came from the wider surroundings of the Lady Mary mine, which is located in the SE corner of the study area (zone III). Two boreholes located close to this abandoned mine site (strongly) violated international and Botswana drinking water arsenic standards, which allow for a maximum of 10 ppb (µg L−1). Yet, the groundwater in the two boreholes featured levels of 26 and 244µg (ppb) As L−1


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respectively. Arsenic is very problematic in the environment because of its relative mobility over a wide range of redox conditions (Smedley & Kinniburgh, 2001). Zinc (Zn), copper (Cu), cadmium (Cd) and nickel (Ni) were also present in very high concentrations. In addition, other compounds such as cobalt, titanium, scandium, antimony, mercury, tellurium, rubidium, and thallium also showed elevated concentrations in zone III. Since zone III is situated in the most downstream spot of the study area, it is likely that all sorts of organic groundwater pollutants and products of anaerobic processes originating from zones I and II were also transferred into this area. Because the concentration of dissolved oxygen was rather high, the redox processes obviously went towards oxidation. The nitrite and nitrate levels were also rather high, which was indicative of active oxidation of ammonia that must have originated from reduced zone II. Sulphate was also very high and possibly originated from the oxidation of FeS or MnS. At the same time the concentrations of Fe2+ and Mn2+ were strongly decreased, which was probably the result of oxidation and the formation of insoluble Fe3+ or Mn4+ compounds. All this suggested very strong bacterial processes. In addition, the Cl distribution in this zone was also indicative of a site characterized by pollution input. All in all, the broad range of organic and highly toxic inorganic pollutants in zone III calls for urgent attention. Another menacing mine site is Monarch (Vogel & Kasper, 2002), which is located north of the confluence of the rivers Tati and Ntshe. Surprisingly though, zone IV did not indicate elevated levels of heavy metals or other trace elements. The only irregularities compared to the surroundings were very high O2 and elevated cobalt and silver concentrations but low nitrate and very low Fe2+ and Mn2+ levels. Possibly this was due to a combination of factors such as limited rainfall in this semi-arid environment, the fine grain-size distribution of the tailings material, and the huge size of the Monarch tailings, which may not easily provide for acid mine drainage (leaching). Rather most of the pollutants may remain in the oxidised crystal form. In contrast, a couple of areas (Ia, IV, IVa, VII), which at first had not appeared conspicuous, revealed strange irregularities in their groundwater composition. Zone IV was very reduced with a medium concentration but high Fe2+ levels. Surprisingly, it also showed a high zinc and a very high chromium concentration. Thallium, rubidium, tellurium, and cadmium were also present in increased concentrations. The distribution of Cl¯ indicated a strong pollution input upstream from this zone. The data obtained from this zone suggested that somewhere there must have been a very strong but unrecognized source of pollution, or else, the natural geological environment may have caused the formation of reduced groundwater conditions and the release of metal ions into the water. The latter was however unlikely given the granitic nature of the resident rock. The situation was similar in zone IVa. A low dissolved O2 level and therefore a low concentration, increased Fe2+ and Mn2+ but also increased arsenic, copper, selenium, beryllium, tin, caesium, yttrium and tungsten concentrations. Data from this site also revealed strong inorganic pollution even though no obvious inorganic waste source was detected. Zone VII was located north of zone IVa. Again, data showed enhanced concentrations of heavy metals but not of the elements identified in zone IVa. Because no pollution


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source could be detected in these two zones it is suggested that remnants of old mine deposits may still exist in these two areas. A small mine dump within zone I (cf. Lehmann, 2001) caused raised concentrations of zircon, tantalum, hafnium, cerium, niobium, bismuth scandium and titanium and it was therefore separated out as mine waste zone Ia. Increased concentrations of Cl¯ and clearly pointed to anthropogenic pollution. The oxygen and nitrate concentrations at this site were strongly reduced but nitrite was increased. This indicated a change in bacterial populations from nitrifying to denitrifying bacteria. Given the obvious similarities in groundwater pollution between the above sites, they were put in the same pollution risk group. They may be even more hazardous than zone III since they are situated upstream from the built-up areas. Clearly, more investigations need to be carried out and immediate attention must be given. 6.3 Waste disposal sites—Zones V and VI Waste disposal sites pose an environmental hazard if they give rise to the formation of leachate plumes. The two most important factors governing the biogeochemical processes within a leachate plume are (1) the redox state, and (2) the content of the leachate. Determining the redox state of polluted groundwater is not easy. It is based on the identification of redox-sensitive species. The primary redox-sensitive species in groundwater are the dissolved ions of Fe2+, Mn2+, , , , , HS¯, the dissolved gasses CH4, N2O and O2, and also some organic substances (Christensen et al., 2001). Most of these processes are driven by bacteria and therefore slow. Bacterial populations are differentiated according to the presence (aerobs) or absence (anaerobs) of oxygen. Hence, a crucial step for this part of the study was to determine the presence of dissolved oxygen (O2) in the groundwater samples. It was obvious that the two waste disposal sites in Francistown were quite different in terms of aeration. The old landfill site (zone VI) was very poor in dissolved oxygen (O2). It is assumed that the long-lasting deposition of waste had formed the reduced environment and that anaerobic processes had probably taken place. In contrast, the new landfill site (zone V) had not yet developed a reduced zone of influence. There the concentration of O2 was quite high. In both zones, Fe2+ and Mn2+ were only present in very low concentrations. Similarly, was also only present in a very low concentration, and and were probably absent. Since no significant increase in Fe2+ and Mn2+ levels and no decrease in could be observed, and given the fact that there was only very little groundwater in both areas (in fact, during pumping one of the sampled boreholes dried up), it is assumed that the geochemistry and the redox states were not governed biologically. Bacteria need water in order to thrive. The very enhanced concentration of sulphate in zone V was probably the result of the presence of oxygenated water and the deposition of ash and building material at this site. Spreading out in a radial manner, sulphate looked like a serious problem. Very


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similar pictures emanated from the spatial concentrations of rubidium, thallium, silver, uranium, molybdenum, lanthanum, zircon, titanium, sodium, bromide, and boron. may have caused The observed slightly enhanced concentrations of CO2 and the dissolution of Ca2+ and Mg2+ out of the carbonates. Probably as a result of this, the concentrations of these two cations were slightly raised (cf. Christensen et al., 2001). This could have influenced the buffering system of the sediments. Both waste disposal sites also featured high Cl¯ concentrations, though the concentration was much wider at the new (zone V) as compared to the old landfill site (zone VI). This supported the assumption that there was no new input of pollution at the old landfill site. So far, the new landfill is only used to deposit inorganic waste. Once it will be used for other kinds of waste, different processes may set in. Considering the semi-arid environment in Francistown it may be assumed that pollution at both landfill sites is localized, will not move readily from place to place, and is probably confined to the soil only. From this it would follow that the two landfills had no significant adverse effect on groundwater quality in the study area. On the other hand, natural remediation in the form of transporting pollutants to other places or through bacterial degradation is also not likely to take place. Thus pollution would probably stay as a hazard for a long time. 7 CONCLUSIONS The study highlighted that groundwater quality in Francistown had deteriorated drastically due to the influence of urban expansion and historical mining. The three dominant sources of pollution were identified as pit latrines, mine waste dumps, and waste disposal sites (landfills). However, pollution from these sources was spatially confined to those zones within which pit latrines, mine waste dumps, and landfills were located. Groundwater from boreholes located within these zones was not suitable for human consumption because it exceeded certain World Health Organization (WHO, 1998) and Botswana Bureau of Standards (BOS, 2000) recommendations for drinking water. Amongst the three pollution sources, pit latrines were found to have had the worst impact on groundwater quality. The chemical analyses of groundwater samples from a total of 48 public and private wells sampled within and around Francistown showed that nitrate concentrations were frequently well above the maximum allowable level of nitrate in drinking water. Groundwater sampled from boreholes situated in remote areas outside the city featured considerably less nitrate. In most cases the nitrate levels in remote areas outside the city were below 40mg/L, which supported the assumption that the cause of nitrate contamination was anthropogenic. Finally, the addition of nitrate through faecal waste had in turn triggered complex redox processes that had raised the ferrous iron (Fe2+) and sulphate concentrations of the groundwater. Mine dumps and/or tailings also contributed to the deterioration of groundwater quality through the addition of heavy metals, and by raising the sulphate concentration in certain zones. However, since the vast majority of the sampled boreholes were located along the rivers Tati and Ntshe and thus far away from the tailings, the real groundwater


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hazards emanating from the tailings may have gone unnoticed. Clearly, further investigations are required. Amongst the three major pollutants, landfills had the least impact on groundwater quality. They are sited away from the main aquifer and within rock formations that yield little groundwater. Because of the limited rainfall in the study area, pollutants within these zones are likely to stay contained within the area. Only occasionally will they be flushed out during the rainy season and become diluted. 8 RECOMMENDATIONS Groundwater from a substantial number of boreholes was found to be not suitable for human consumption. It is therefore necessary to determine which boreholes are used for humans so as to discontinue their use. As a rule, the Francistown city council ought to adopt a development strategy that places more emphasis on an environmental approach to planning taking into account the existing water resources. For example, all new infrastructures should be placed as far away as possible from the rivers because the aquifers in the area are dependent on rainfall and river recharge. Activities such as the recent aligning of the sewage pipelines along the riverbanks must in future be avoided by all means. Such activities not only destroy a natural flood barrier but they may in fact lead to serious water pollution. Similarly, any new development must not include pit latrines. Since a sewage reticulation system has been put in place throughout the city, it is necessary to educate the residents on the need to connect to the sewerage and put an end to the use of pit latrines. So far, connection to the sewerage system is on a voluntary basis and pit latrines (and septic tanks) are currently still the main means of wastewater discharge in the newly connected areas. The study also confirmed that environmental and health hazards emanating from abandoned mine tailings must be dealt with in a way that guarantees human safety and environmental protection. The reported chemical “cocktail” conditions of tailings and the observed trace element concentrations in some boreholes make this obvious. The waste disposal (landfill) sites appeared to have been well sited in areas of low groundwater yields. But continuous monitoring is necessary in order to determine the dynamics of possible plume development so as to act upon possible groundwater pollution. Further investigations are also necessary to determine the source of heavy metals and other pollutants at the new landfill site. REFERENCES Colquhoun, B., O’Donnel, H. & Partners 1974. Redevelopment of the Francistown groundwater studies report. Phases I, II and III. Australian Groundwater Consultants. BOS 2000. Water quality—Drinking water—Specification. BOS 32, Botswana Bureau of Standards, Gaborone, Botswana. Christensen, T.H., Kjelsden, P., Bjerk, P.L., Jensen, D.L., Christensen, J.B., Baun, A. Albrechtsen, H.J. & Heron, G. 2001. Biogeochemistry of landfill leachate plumes. Applied Geochemistry: 659–718.


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Gibb, A. Sir & Partners 1987. Francistown Water Development. Pre-Investment Study. Appendices B1 and B2. Water Resources. Water Utilities Corporation, Botswana. Key, R. 1976. The geology of the area around Francistown and Phikwe, Northeast and Central Districts, Botswana. District Memoir 3, 121p. plus maps, Dept. Geological Survey (DGS), Lobatse, Botswana. Lehmann, A. 2001. Conceptual map of the urban soils of Francistown. Draft map and explanations with special reference to town planning and environmental quality. Report by the Environmental Geology Division, Dept. of Geological Survey (DGS), 48p, Lobatse, Botswana. Smedley, P.K. & Kinniburgh, D.G. (2001). Source and behaviour of arsenic in natural waters. In: United Nations Synthesis Report on Arsenic in Drinking Water. Vogel, H. & Kasper, B. 2002. Mine soils on abandoned gold mine tailings in Francistown. Report by the Environmental Geology Division, Dept. of Geological Survey (DGS), 43p., Lobatse, Botswana. WHO (1998). Guidelines for drinking water quality. World Health Organization, 2nd ed., Volumes 1 and 2, Geneva, Switzerland.

In situ remediation potential for Southern African groundwater resources Sumaya Clarke, Gideon Tredoux & Pannie Engelbrecht Water Programme, Environmentek, CSIR, Stellenbosh Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: In situ groundwater remediation is practised in Europe, the United States, New Zealand and Canada. Widely accepted treatment methods include, permeable reactive barriers, redox manipulation, the Vyredox® method and biological denitrification. The permeable reactive barrier is widely used for contaminant removal. It consists of a constructed trench filled with a contaminant specific reagent, such as sawdust or wood chips for the promotion of biological denitrification. Other techniques include in situ redox manipulation which requires dithionite injection and in situ biological denitrification, which uses substrates such as ethanol or methanol. The Nitredox® and Vyredox® methods use a sophisticated arrangement of injection and aeration boreholes to manipulate oxidation and reduction to control nitrate, iron and manganese concentrations in the aquifer. Concern about nitrate as a chemical constituent of groundwater is increasing, especially in the arid and semi-arid regions of Southern Africa. Livestock losses, and “blue baby syndrome” in humans, result from high nitrate concentrations in drinking water. Hence, there is a need to remediate groundwater with nitrate concentrations above the required standard. Low cost, robust and simple treatment technologies are needed for rural water supply in Southern Africa. This paper gives an overview of the performance of full scale and pilot scale treatment plants. An estimate was made of the costs of applying selected in situ treatment options for a South African town. The order of difference in cost between in situ and ex situ treatment plants is calculated. The geological and hydrogeological parameters required for successful operation of most in situ treatment systems are described. Advantages and disadvantages of in situ treatment are also mentioned.


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1 INTRODUCTION Research into groundwater remediation methods has been intensified and various techniques have been tested and applied. “Pump and treat” technologies have been widely used in the USA. The success of this method has been questioned, considering its excessive costs, (Simon et al., 2001). As an alternative, in situ technologies are being developed and applied for removing contaminants in the aquifer. Literature references to more than 100 successfully operating sites confirm that permeable reactive barriers can remove a variety of contaminants including halogenated organic compounds, metals, nitrates, acid mine drainage, phosphorous, chromium and gasoline/petrol derivatives using various reactive materials in the barrier. The currently operating sites range from household scale permeable reactive barriers to industrial sites, to mining and wastewater treatment plants and municipal well fields (Robertson and Cherry, 2003). Slowly degradable carbon sources are placed in barriers perpendicular to the flow and such treatment occurs with a high success rate. The Nitredox® plant in Vienna, Austria to treat nitrate, iron and manganese; has been operated successfully for more than a decade. Various low cost, robust treatment techniques like permeable reactive barriers and biological denitrification have proven to be successful in Canada, New Zealand, Austria, France, and the USA. Cost implication of implementing any in situ technology is important and need to be taken

Figure 1. Map showing the distribution of nitrate (as NO3) in Southern Africa.

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into consideration. A cost estimation, performed for a town in the Northern Cape Province, South Africa demonstrates the cost difference between in situ and ex situ treatment methods. Internationally a nitrate concentration of 10mg/L as N (45mg/L as NO3) is accepted as guidelines for health risk. The maximum allowable level is set as 20mg/L as N (90mg/L as NO3) in South Africa. Nitrate concentrations in groundwater are alarmingly high in some parts of Southern Africa as shown in Figure 1. The northern provinces of South Africa all have many groundwater sources with nitrate concentrations ranging from 251– 500mg/L. In some areas concentrations up to 1000mg/L occur, while the Southern Kalahari has concentrations of up to 2000mg/L, particularly in the more saline areas, (Marais, 1999, Tredoux et al., 2000). In view of the prevalence of nitrate in groundwater, this paper focuses on in situ denitrification as a viable treatment option for town and rural applications. It is crucial that groundwater pollution be taken seriously, and that remediation and protection of the groundwater resources available be considered as a priority in countries affected by pollution. Surface water resources are limited, more particularly in arid and semi arid regions, and with groundwater being unfit for use by inhabitants of these regions, a serious threat is posed to the survival and growth of communities affected. 2 AVAILABLE DENITRIFICATION TECHNOLOGIES Many methods are successfully being employed to denitrify groundwater. Permeable Reactive Barriers and Biological Denitrification methods are the most widely used of the many methods identified, hence these methods will be discussed in further detail. 3 PERMEABLE REACTIVE BARRIERS Permeable reactive barriers (PRB) are constructed across the flow path of the migrating plume of contaminated groundwater. These systems are typically designed as a continuous trench, filled


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Figure 2. Permeable reactive barrier in situ denitrification system, shown here on a rural/local scale. with permeable, reactive material. Alternatively, a funnel and gate configuration is used, which includes impermeable sections, directing the groundwater flow through the permeable treatment “gates” (Robertson and Cherry, 1995, 2000, Blowes et al., 2000, Schipper & Vojvodic-Vukovic, 2000). These treatment systems may be applied for the removal of various anions, cations, organic compounds and inorganic compounds. Configurations and system design is generally site and contaminant specific, e.g. for mitigation of nitrate at on site sanitation (see Fig 2). Requirements for the denitrification barriers (“walls”) include the following: ● The site should have a shallow water table; ● Aquifer parameters should be well understood; ● The aquifer thickness and composition should allow for constructing the wall i.e. not more than 10m deep. ● Boreholes should be placed on either side of the wall to sample groundwater to monitor chemical and microbiological changes. ● Analysis of groundwater and soil should be done prior to installation of the PRB to estimate the amount of carbon substrate required.

4 BIOLOGICAL DENITRIFICATION Biologically enhanced denitrification requires injection of readily available carbon substrates such as ethanol, methanol, sucrose and glucose to serve as a source of energy for promoting microbiological activity. Various configurations of the method may be


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used to suit site-specific requirements. The most successful configurations are those used in Vienna and Nebraska. A list of operational systems is presented in Table 1. The daisy configuration is shown in Figure 3. Most of the biological denitrification systems use variations of this basic configuration. The area in the sketch labelled (IV) represents nitrate polluted water. The “daisy” represents the area (in plan view) progressively affected by the denitrification due to substrate (carbon source) injection. The reaction takes place in zone I, followed by filtration of any by-products in zone II while the nitrate free water (or water with a lowered nitrate concentration) is found in zone III. The Nitredox® system consists of one pumping borehole located at the centre of two concentric circles of injection boreholes. It involves injection of an organic substrate (outer ring) to enhance denitrification, but includes an additional phase of aerated water injection for the oxidation and removal of iron (inner ring) once the nitrogen is removed. The groundwater recovered from the

Table 1. Some pilot and field operational denitrification sites and their experiences. Method and Period NO3location Nmg/L

Aquifer

Carbon substrate

Injection/ barrier

Nitrate removed

PRB, Canada 5 yrs+ 5–57 Primary Sawdust/ Emplaced 58–91% (1) woodchips barrier PRB, New 5 yrs+ 5–15 Unconfined, Sawdust Emplaced 95+% Zealand (2) sandy barrier Electrokinetics/ Test Controlled Primary/ None: Abiotic Emplacement 84–87% Fe-wall, period amounts secondary of wall and USA(3) electrodes NitrEI system, Many Up to Primary/ None: Electrodes Reduced Canada (4) Currently 1000 unsaturated Electrochemical down to operating zone electrodes 0.1mgN/L sites Daisy wheel, 40 Sand and Ethanol C and P 35%-cISBD, gravel injection injection; Nebraska (5) 90–100% pinjection Nitredox, 15 years 14 Primary Ethanol P injection 75% ISBD, Vienna aquifer (6) ISBD, line of 226–565 Chalk Ethanol 80% injection boreholes, France (7) C-Continuous injection, P-pulse injection. (1) Robertson and Cherry (1995, 2000), Blowes et al., (1999), (2) Schipper & Vojvodic-Vukovic, 2001, (3) Chew and Zhang, 1998 and Loo, 2000, (4), (5) Khan & Spalding (1998), (6) Braester and Martinell (1988), Jechlinger et al., (1991), (7) Chevron et al., (1998).


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Figure 3. Biological denitrification treatment system with “daisy” configuration (after Mercado, 1988). Table 2. Cost estimation of implementation of in situ denitrification compared to ex situ treatment (amounts in S A Rand). Method

PRB ISBD Ex situ Method

Capital investment Operation and maintenance per m3 Projected running expenses over 5 yrs Projected total cost over 5 yrs

61332 100289 350000 0.1 0.3 2 71144 21343 2845740 132476 313720 3195740

central production borehole is partly free of nitrate but completely free of iron, manganese or other by-products (Braester and Martinell, 1988). This method has been applied to coastal aquifers and primary aquifers. Where biological denitrification is implemented, it is important to know and monitor the permeability and porosity. Clogging may result when the carbon substrate injection exceeds the amount required for denitrification. The method has been applied mainly to primary aquifers where flow dynamics are well understood.


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5 OPERATIONAL SITES In Southern Africa, denitrification per se is not applied. Treatment methods use expensive ex situ pump and treat systems such as desalinisation by ion exchange. These do not specifically treat nitrate and does not obtain optimum results with respect to nitrate concentrations. There is a number of test and full-scale in situ denitrification plants all over the world. Table 1 lists some of these sites, their experiences and shows the variety of configurations, carbon sources and aquifer types to which in situ denitrification has been applied. These methods are mainly applied in sand; gravel and other primary aquifer type settings, although it has been used in chalk aquifers as well. Implementation in secondary aquifer settings is said to be possible and has been modelled for sites in the UK (Cartmell et al., 1999). 6 OPERATIONAL EXPERIENCES The PRB systems in Canada have been operational for more than 5 years and are used on various scales including household, municipal, and huge water treatment plants. In New Zealand, the reactive barrier had to be replaced after 5 years of operation as reactive material had clogged parts of the aquifer. In the USA, the electrokinetic methods worked better when combined with iron walls. The biological denitrification used in Nebraska used both continuous and pulse injection regimes. The continuous carbon source injection was more efficient in denitrification but led to complete biofouling after 10 days. The system used inner oxidation ring to remove possible nitrite, iron and manganese. In Vienna, where the Nitredox® method is currently operational, clogging was experienced. Pulse injection and reduction of the amount of ethanol (carbon source) prevented clogging of the system. In France, natural in situ denitrification was carbon limited. Remediation by carbon source addition was selected to accelerate denitrification. Denitrification was achieved in long time operation (450 days). Rates of denitrification were improved when trace metals were supplied in conjunction with the carbon substrate. 7 ECONOMIC FEASIBILITY OF TREATMENT TECHNOLOGIES The costs of implementing denitrification were estimated for Marydale in the Northern Cape Province of South Africa. The results are shown in Table 2. In situ application was compared with a conventional ex situ method. In Marydale, a well field containing 10 boreholes is used as the town water supply. Half of these boreholes, produce groundwater of nitrate concentration above the maximum allowable 20mg/L, (Hofmann, 1997). Microbiological sampling showed that coliform counts of 15/100ml in some boreholes were three times as much as the SABS specification (Hofmann, 1997). No faecal


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coliforms were detected. This gives an indication that no human or animal waste reaches the boreholes. Exploration boreholes drilled in the area revealed that a primary and a secondary aquifer are present in the area. The secondary fracture system is not well understood, but it is believed that the bed rock is not very permeable. The main water bearing unit is the alluvial cover of more or less 12m thick. The aquifer material consists of sedimentary layers containing primarily sand and silt. The Projected water demand of the town for 2005 is 142287m3/a (Shand and VSA, 1997). Capital expenses for permeable reactive barriers (PRB) include excavation costs, wall emplacement costs and dewatering prior to wall emplacement. Woodchips or sawdust was considered as suitable permeable reactive barrier material as these are cheap and slowly degradable carbon sources. The barrier size is based on the size of the well field and the depth to bedrock. The largest contribution to capital costs for in situ biological denitrification (ISBD) methods include borehole construction costs, purchasing of injections pumps among other costs. Erecting infrastructure is a major expense for conventional treatment plants. Running costs were based on the projected annual water demand and estimated chemical costs. The PRB method requires limited maintenance. In the calculation, operation and running costs are included; however, they may not occur frequently for methods like PRB. Operational and maintenance costs are relevant especially when clogging or partial clogging of wells occurs. Pump and treat methods and other ex situ methods (in this case ion-exchange) generally cost an order of magnitude more than in situ methods. It is clear from this information that rural communities for which funding is not always in surplus may capitalize on this advantage as well as the ease of use of some of these methods. Proper management and monitoring of sites are essential to detect potential clogging cases early and to put remedial measures in place. 8 DISCUSSION Field scale plants have proven in situ technologies to be successful. The nitrate removal rate at most currently operating sites are high. It is evident from Table 2 that the permeable reactive barrier method is the most cost effective method. Capital costs are relatively low and it requires little or no additional treatment of groundwater after passing through the system. Installation and running costs of ex situ treatment exceed that of in situ methods. Operational sites in the US, Canada and New Zealand showed that barrier material replacement was only required after 5 years, while ex situ methods have set running expenses per cubic meter of water. The largest full-scale in situ denitrification plant uses the Nitredox® principle. This plant is located at Bisamberg, Vienna (Austria) and has been operating successfully for more than a decade (Jechlinger et al., 1991). It uses ethanol as the carbon substrate and the process is regulated to ensure that the raw water nitrate, which exceeds 65mg/L, is reduced to approximately 35mg/L in the product water. There are advantages as well as some disadvantages of in situ treatment technologies. Some advantages of implementing such a treatment system include minimal exposure to


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dangerous chemicals, job creation in rural villages, little or no treatment required at the surface, possible treatment of other contaminants due to redox changes, costs savings in comparison to conventional ex situ treatment plants, low maintenance costs, simple to use technologies, and no need for electricity (PRB- method). Disadvantages include possibilities of clogging of boreholes. This occurs when the carbon dosage is in excess of the required amount. Sulphate reduction may occur when carbon substrate dosage is too high and result in acetate production as a by-product of microbial activity (Israel, 2004, unpublished data). Loss of hydraulic permeability of the aquifer is possible if carbon addition is not effectively managed. Preferential flow of groundwater can occur, where a great contrast develops between the treatment zone and the rest of the aquifer and the path of least resistance is taken by the groundwater. Hence monitoring of the above mentioned parameters is very important. Cautionary measures include proper estimation of the required amount of carbon substrate, and monitoring the effective porosity and permeability of the aquifer before, after and during treatment. Management of implementation and monitoring are essential for success. It is important to note that no microbes are added to initiate the process, as this would affect the ecosystems that are already established at any specific site. There are many strains of bacteria that occur naturally under the various environmental conditions, which are capable of denitrification. Although some scientists may prefer to add appropriate bacteria to initiate the process but the addition of a carbon source is sufficient to activate resident bacteria. 9 CONCLUSION In situ groundwater treatment methods are widely used and accepted in the US, Canada, Europe and New Zealand. Literature shows that various in situ methods for a range of heavy metals, organic compounds and other constituents have been successfully implemented at field scale in these countries. In situ denitrification methods are also viable treatment methods which are successfully implemented and currently operating. The cost analysis performed in South Africa, showed that there is an order of magnitude difference between the costs of ex situ and in situ treatment plants. Optimal conditions for most in situ treatment methods include the following: ● Primary aquifer systems, or well understood secondary aquifers (with respect to flow characteristics and porosity/permeability). ● Aquifer material can include sand, gravel, and chalk material. ● A known concentration of nitrate-nitrogen is important for estimation of the appropriate quantity of carbon substrate. ● A maximum aquifer thickness of 20m for injection type methods (e.g. ISBD) and 10m for emplacement methods (e.g. PRB). ● Monitoring of aquifer parameters (permeability, hydraulic conductivity etc.), chemical changes (pH, Eh, etc.) and microbiological changes with time. It is important to note that no foreign microbes are added, as this would affect the ecosystems that are already established at any specific site. Although some scientists may


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prefer to add appropriate bacteria, addition of a carbon source is sufficient to activate resident bacteria. REFERENCES Blowes, D.W., Ptacek, C.J., Benner, S.G., McRae, C.W.T., Bennett, T.A. & Puls, R.W. 2000. Treatment of inorganic contaminants using permeable reactive barriers. Jnl. of Contaminant Hydrology, 45:123–137. Braester, C. & Martinell, R. 1988. The Vyredox and Nitredox method in situ treatment of groundwater, Wat. Sci. Tech., 20(3):149–163. Cartmell, E., Clark, L., Oakes, D., Smith, S. & Tomkins, J. 1999. Feasibility of In situ Bioremedition of Nitrate in Aquifer systems, R & D Technical Report P277, WRC report no. EA 4683. Chevron, F, Lecomte, P., Darmendrail, D. & Charbonnier, P. 1998. Rehabilitation de qualitè physicochimique d’un aquifere contaminepar des nitrates d’origine industrielle- un example en region Nord-Pas de Calais. L’Eau, L’Industrie, Les Nuisances, 208(31–35) (In French). Chew, C.F. & Zhang, T.C. 1998. In situ remediation of nitrate contaminated ground water by electrokinetics/ iron wall process. Water Science and Technology, 38(7):135–142. EPA, 1995. In situ remediation technology status report: Treatment walls. Report No. EPA/540/K94/004. Office of Solid Waste and Emergency Response, US Environmental Protection Agency. Israel, S., 2004, Subsurface Manipulation of the Nitrogen Cycle: In-Situ denitrification and its potential for remediation of contaminated soil and ground water resources: Case Study: Marydale, Northern Cape, MSc research, unpublished data, University of Stellenbosch. Jechlinger, G., Schöller, F., Seidelberger, F., & Zibuschka, F. 1991. Denitrification In Situ. In: Proc. of I.W.S.A workshop: Inorganic nitrogen compounds and water supply. Hamburg, 27–29 Nov:113–122. Khan, I.A., & Spalding, R.F. 1998. Denitrification using a daisy well system. Presentation to National Sanitation Foundation International Symposium, Safe Drinking Water in Small Systems: Technology, Operations, and Econimics. Washington D.C., May 10–13. Kruithof, J.C., Van Paasen, J.A.M., Hijnen, W.A.M., Dierx, H.A.L. & Van Bennekom, C.A. 1985. Experiences with nitrate removal in the eastern Netherlands. Proc. Nitrates Dans les Eaux, Paris 22–24 October. Loo, W.W. 2000. Electrokinetic treatment of hazardous wastes. Standard Encyclopedia of Environmental Science and Technology, New York, McGraw Hill,: 14.69–14.84. Mercado, A., Libhaber, M. & Soares, M.I.M. 1988. In situ biological groundwater. denitrification: Concepts and preliminary field test. Wat. Sci. Tech., 20(3):197–209. Ninham Shand and VSA Consulting, 1997, Geohidrologiese Ondersoek van die Groundwaterbronne by Marydale, Noord-Kaap Provinsie, VSA Conculting pty. Ltd. Robertson, W.D. & Cherry, J.A. 1995. In situ denitrification of septic system nitrate using reactive porous media barriers: Field trials. Ground Water, 33(1):99–111. Robertson, W.D., Ford, G. & Lombardo, P. 2003. Wood-Based Filter for Nitrogen Removal in Septic Systems, (Submitted to: Journal of Environmental Quality), (unpublished). Schipper, L.A. & Vojvodic-Vukovic, M. 2000. Nitrate removal from groundwater and denitrification rates in a porous treatment wall amended with sawdust. Ecol Engineering, 14:269–278. Schipper, L.A. & Vojvodic-Vukovic, M. 2001. Five years of nitrate removal, denitrification and carbon dynamics in a denitrification wall. Wat. Res. Research, 35(14):3473–3477. Tredoux, G, Talma, A.S. & Engelbrecht, J.F.P. 2000. The increasing nitrate hazard in groundwater in the rural areas. Paper presented at WISA 2000, Sun City, RSA, May 2000.

Coastal aquifers intrusion at semi-arid region of Turkey L.Yilmaz Technical University of Istanbul, Civil Engineering, Hydraulic Division, Maslak, Istanbul, Turkey Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: Coastal aquifers are important sources of water for domestic, agricultural and industrial uses. Under natural conditions the hydraulic gradient is towards the sea so that there is a natural outflow of fresh groundwater. Frequently the hydraulic gradient is small. Therefore very little extraneous activity is required to disturb the natural system and cause the fresh water to become. This situation poses a difficult management problem which is best addressed by means of mathematical models. This research describes the use of such models together with the difficulties likely to be encountered.

1 INTRODUCTION 1.1 Relationship between the level of the water table and the depth to the saline wedge A relation between the level of the water table and the depth to the saline wedge in an unconfined aquifer under steady conditions of flow (Badon Ghijben, 1889; Herzberg, 1901, Davis, 1978) points out that Joseph DuCommun (1828) made similar observations. Prior to the work of these pioneers it was thought that saline water occurred at a depth close to sea level. The saline water close to the sea shore is defined by Badon GhijbenHerzberg equation, which was derived by a simple application of hydrostatics. The weight of a column of fresh water of height hf+z is equal to the weight of a column of saline water of height z. If rof and ros are the densities of fresh and saline water respectively, it is given in equilibrium conditions rosgz=rofg(hf+z) (1) or (2) If the relative densities of fresh and saline water are taken as 1.0 and 1.025 respectively, then


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z=40 hf (3) This expression is a good approximation in steady state conditions when the zone of dispersion is only a small fraction of the saturated thickness of the aquifer. Since fresh water is flowing along the interface some mixing will occur due principally to microscopic and macroscopic dispersion. When the saline and fresh water mix in the zone of dispersion then the diluted saline water becomes less dense and will rise along a seaward path. The resulting mechanism is similar to thermal convection, the only difference being that the gradients are caused by changes in density due to changes in salinity instead of temperature (Cooper, 1964). This flow will advect some saline water towards the sea. Therefore, in order to preserve the saline mass balance, a small flow of saline water must occur in the landward direction. This flow creates a head loss, thus a reduction in pressure at the interface and a reduction in the level of the interface. This application gives the position and movement of a saline front in a coastal aquifer. 1.2 Groundwater flow equation Using the Darcy’s law and the law of conservation of mass to a control volume, (Pinder and Bredehoeft, 1968; Konikow and Bredehoeft, 1978) gives (4) where Tij=transmissivity tensor (L2T−1) h=hydraulic head (L) above a reference point S=storage coefficient (−) W=source or sink volume flow term (LT−1), positive for outflow (=W (xi, t), i=1, 2. This is usually the recharge, pumping and evapotranspiration). xi, Xj=Cartesian coordinates (L) t=time (T) The advection-dispersion equation is given using the notation of Konikow and Bredehoeft (1978) as; ∂(Cb)/∂t=∂/∂xi(bDij∂C/∂xj)−∂/∂xi(bCVi)−C′W/ε (5) where Dij=coefficient of hydrodynamic dispersion (L2T−1) Vi=seepage velocity in the direction xi (LT−1) C=concentration of the pollutant (ML−3) C′=concentration of the pollutant in the source or sink fluid (ML−3) b=saturated thickness of the aquifer (L) E=effective porosity of the porous medium (−) This equation gives the change in chemical concentration due to kinematic dispersion and diffusion, the effect of advective transport and the removal of pollutant due to fluid sources and sinks.

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2 MAIN OBJECTIVE 2.1 Solutions of the groundwater equations Therefore the interface is not sharp and a mixing zone exists, the thickness of which depends upon the hydrodynamics of the aquifer. If this transition zone is only a small fraction of the saturated thickness of the aquifer then the assumption of a sharp interface is reasonable and a good mathematical description of the shape of the saline wedge can be obtained. The thickness of the fresh water wedge decreases in the seaward direction and the slope of the water table steepens towards the coast. Therefore the shape of the interface is concave upwards. If the more realistic view is taken that the fresh and saline water are miscible, then the interface cannot be sharp and the mathematical description of the problem becomes more complicated. The assumption of a sharp interface cannot be considered reasonable if the flow situation varies with time since the hydrostatic pressure distribution will vary and the assumed interface will move either landwards or seawards. This results in the sharp interface being replaced by a zone of dispersion in which the salinity of the water varies from fresh to very saline. Clearly the simplifying assumption of a sharp interface makes for a mathematically simpler but less accurate model. 2.2 Sharp interface models The relationship between groundwater levels and the depth to the saline wedge is given by Badon Ghijben and Herzberg who, working independently, developed a relationship between the level of the water table and the depth to the saline wedge in an unconfined aquifer under steady conditions of flow (Badon Ghijben, 1889; Herzberg, 1901). Davis (1978) points out that Joseph DuCommun (1828) made similar observations. Prior to the work of these pioneers it was thought that saline water occurred at a depth close to sea level. In contemporary practice the result is always referred to as the Badon GhijbenHerzberg equation. This equation is derived by a simple application of hydrostatics. Since the interface is stationary then the weight of a fresh water above the interface is exactly balanced by the pressure of the saline water below the interface. By consideration of the Figure it can be seen that the weight of a column of fresh water of height hf+z is equal to the weight of a column of saline water of height z. If rof and ros are the densities of fresh and saline water respectively, then for equilibrium rosgz=rosg(hf+z) (5) If the relative densities of fresh and saline water are taken as 1.0 and 1.025 respectively, then z=40 hf (6) This simple expression gives a remarkably good first approximation to the depth below sea level of the interface under steady state conditions when the zone of dispersion is only a small fraction of the saturated thickness of the aquifer.


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This concept can be further developed to determine the extent of the penetration of the saline wedge inland. Many analyses can readily be developed, for example the determination of the shape of the interface when the seepage surface is submerged beneath the sea (Glover, 1964) and the shape of the saline upcone beneath a pumping well in a coastal aquifer (Schmorak and Mercado, 1969; Sahni, 1972). 2.3 A sharp interface with some mixing When a sharp interface is assumed, then this interface is a flowline in the same way as the water table is a flowline. Hence it is a boundary condition for the problem. Since fresh water is flowing along the interface some mixing will occur due principally to microscopic and macroscopic dispersion. When the saline and fresh water mix in the zone of dispersion then the diluted saline water becomes less dense and will rise along a seaward path. The resulting mechanism is similar to thermal convection, the only difference being that the gradients are caused by changes in density due to changes in salinity instead of temperature (Cooper, 1964). This flow will advect some saline water towards the sea. Therefore, in order to preserve the saline mass balance, a small flow of saline water must occur in the landward direction. This flow creates a head loss, thus a reduction in pressure at the interface and a reduction in the level of the interface as predicted from the Badon Ghijben-Herzberg equation. The mechanism is shown in Figure. It is possible to extend these concepts to determine the solutions to various moving interface problems. However, except for some very restrictive cases, analytical solutions do not exist. Hence numerical methods are required to solve the resulting equations, which usually means that it is more convenient to use commercially available groundwater quality models. Approximate solutions for moving interface problems, including numerical ones, are discussed by Bear (1979). 2.3.1 Equations of groundwater flow and advection—dispersion The above section dealt with some very simple first approximations for determining the position and movement of a saline front in a coastal aquifer. Whilst these are useful in the early stages of a study they do not permit a full solution to the majority of aquifer problems. For example they cannot deal with spatial variations of geology or aquifer parameters nor with multi-layered aquifers. In order to achieve this two equations are required, one to describe the groundwater flow and one to describe the movement of the salt. These will be considered in turn. 2.4 Solutions of the groundwater equations The finite difference method is used for solving this type of differential equations. The first step is to give the area of the model in mathematical terms, which is called the solution domain. This solution domain is covered by a rectangular grid which can be either regular or irregular. The differential equation is replaced by a set of difference equations, one for each grid point. This results in n×m simultaneous equations which have to be solved, where n is the number of rows and m is the number of columns of the

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grid. The finite difference method is, perhaps, the most frequently used technique for solving the flow equation. However, it is not often used to solve the advection-dispersion equation because of a phenomenon known as numerical dispersion. The numerical solution usually appears to advance the solute at a rate which is greater than is physically possible. Finite difference schemes can be developed to minimize dispersion. However they are liable to cause either overshooting or undershooting which appear in the solution as oscillations. Van Genuchten (1976) analyzed and gave as a result that the finite element schemes will usually yield more accurate solutions than finite difference ones. There are some rules which can be helpful in minimizing the effects of dispersion. These use a form of the Peclet number, Pe, and the Courant number, C. The grid should be designed such that Pe(=dx/De)75

Number of respondents Chitakatira Nyanyadzi (n=121) (n=181) 29 46 34 10 1

22 42 32 17 3

Respondents did not make a distinction between clean and safe water although the general perception was that clean and safe water was free of bacteria. Table 3 gives perceived characteristics of clean and safe water.

Assessing demand for clean and safe domestic water in eastern Zimbabwe

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The perception of whether water was clean or safe was influenced by the source of the water and the season in which that water was used as shown in Table 4. In the wet season, across all water sources, water was perceived to be unsafe. 3.3 Willingness and ability to pay Eighty-two percent of the respondents felt that primary water use should be accessed free of charge, and 79.5% of the respondents felt that people had to pay for commercial use of water. Some 2.1% of the respondents felt that water had to be paid for to enable the maintenance of

Table 2. Patterns and classification of water uses. Water use Drinking Cooking Bathing Laundry Irrigating gardens Livestock watering Brick making Irrigating plots

Classification (%) % citing Primary Commercial water use 99.2 99.2 99.2 99.2 80.8

98.3 54.4 98.7 98 70.3

0.8 0.4 0.4 0.8 10.9

31

16.7

14.3

23.4 25.9

9.2 7.9

14.6 18

Table 3. Characteristics of clean and safe water. Characteristic % attributing % attributing it it safe clean Clear Bacteria free Chlorinated Protected Tasty Not rusty Not dirty Piped Treated

43.1 34.3 3.8 9.6 1.3 0.4 0.4 0.4 0.8

38.1 36.4 3.8 9.6 1.3 0.4 0 0 2.9


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Table 4. Perception of water quality of various sources across seasons. Water quality in Water quality in summer (%) winter (%) Water Safe Not Clean Not Safe Not Clean Not source safe clean safe clean Borehole Deep well Shallow well River Dam Canals and water taps

66.1 1.3 6.7 2.1

67 6.7

0.4 53.1 1.7 2.1 3.3 1.3

53.6 3.3

1.3 1.3

0.4 2.1

0.4

2.1 0.4 1.3

0.4

1.3

4.2 31.8 3.3 5 25.5 1.7

5.4 30.5 3.3 12.6 2.5 5.9 2.9 3.3 25.3 1.7 16.7 1.7

4.6 11.3 2.1 4.2 16.7 1.7

infrastructure. About 80% of the respondents said it was the responsibility of the government to ensure that the communities had enough water. Domestic water provision was said to involve some cost by 28.9% of the respondents. Of these, 4.8% put the costs as ranging between Z$50 and Z$400 (Z$4000=US$1). This was however misleading since the figures coincided with the monthly water bills for respondents, especially those staying at rural service centres. The ability to pay different sums of money for water for the month is as shown in Figure 1. Ability to pay, it should be noted, is a function of affordability. It, however served, as a good indicator of respondents’ demand since it showed the price respondents would want their water supplied at. It was observed that generally the number of respondents decreased with the increase in the amount to be paid. However Z$10 was the most common WTP figure. Ability to pay was linked to the SPP and MWTP, which was affected by a number of factors such as the source of the water, the season and the treatment water was subjected to. 3.4 Factors affecting SPP and MWTP A regression model to find the effect of rainfall received (β1), season (β2), gender (β3), age (β4), occupation (β5) and access to piped water (β6) on the SPP and MWTP was run at 5% significance level. The general model was defined as: SPP/MWTP=a+β1+β2+β3+β4+β5+β6+ (1) The following hypotheses were then formulated to test the assumption of normality on equal variance using the Levene’s test. H0: δ12=δ22=δ32=δ42=δ52=δ62 (2)


(homogeneous variance) H 1: δ12≠δ22≠δ32≠δ42≠δ52≠δ62 (heterogeneous variance)

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(3)

Accept H0 if p>0.05 Further analysis was undertaken using non-parametric tests, namely the MannWhitney, the Moses and the Kruskal-Wallis.

Figure 1. Respondents’ ability to pay for domestic water per month. Table 5. Comparison of respondents’ MWTP in different seasons. MWTP range (Z$/bucket—25 litre container) 0 1–20 21–40 41–100 >100 Source S W D S W D S W D S W D S W D of water Shallow 8.8 7.9 7.1 33 32.9 33.9 0.4 0.8 1.3 0.4 0.8 1.3 0 0 0 well


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Deep 6.7 5.9 5.4 12.6 22.6 23.4 0.4 2.1 0.8 0 0 0.8 0.4 0 0.4 well Borehole 4.6 5 4.2 34.8 31.8 33.1 1 7 4.3 1.3 2 1 1.7 2.5 0.8 1.3 1 7 River 9.6 8.8 7.9 17.5 18 19.3 0.4 0.4 0.4 0.8 1.3 1.7 0 0 0 Dam 7.9 7.9 6.3 18.7 17.9 18.9 0 0.4 0.4 0.8 1.3 2.1 0.4 0.4 0.4 Piped 2.5 2.5 2.5 48.9 47.6 45 2.5 2.9 4.2 8.2 8.7 9.5 2.1 2.5 2.8 scheme Canals 0.4 0.4 0.4 2.1 2.1 2.1 0 0 0 0.4 0.4 0.4 0 0 0 & water taps Key: S—Summer; W—Winter; D—Drought; MWTP— Maximum willingness to pay.

Rainfall: There was a significant effect of rainfall received in a particular area on the demand for clean and safe water. Chitakatira generally had lower SPP and MWTP values compared to Nyanyadzi. Water was therefore perceived to be more valuable in the generally drier Nyanyadzi than in the wetter Chitakatira. The ANOVA test on the means showed that except for the SPP and MWTP to repair broken down pipes, all other variables were significantly affected by the amount of rainfall received. The MannWhitney test confirmed that the amount of rainfall had an effect on all variables except the SPP for repairing a broken down pipe. The Moses test showed that all variables, except the SPP and MWTP for establishing a new borehole, had major differences within them because of the rainfall factor. The amount of rainfall received in a particular location can therefore be said to influence respondents’ WTP. Source of water: Water from boreholes, piped water schemes, canals and water taps, shallow and deep wells had a modal MWTP figure of Z$10 whilst that of dam and river water was Z$0. Piped water was the most popular water source followed by borehole, shallow well, deep well, river, dam, canals and water taps. Season: The measures of association between season and the different variables were also very small (ranging between 0.015–0.098) confirming minimal association between season and the SPP and MWTP values. However, drought had the highest mean followed by winter and summer. Table 5 shows the distribution of respondents’ MWTP across the seasons. Water treatment: Treatment of water marginally changed the proportion of respondents willing to pay more than Z$40 across all the water sources, especially for piped, river and dam water. When treatment was factored in, the modal MWTP figures remained the same for the respective water points although the MWTP figures rose to Z$999. The proportion of respondents willing to pay Z$40 or less actually increased for water sources such as the piped scheme and river, whilst it decreased in the case of water from boreholes, shallow and deep wells. The modal MWTP figures for different water sources did not change. The distribution of respondents’ MWTP with and without treatment is shown in Tables 6 and 7. Gender: The ANOVA, Mann-Whitney and Moses tests revealed that gender did not significantly affect the SPP and MWTP values of the respondents. Except for the SPP and MWTP of establishing a new borehole and repairing it, all other variables showed that males had higher mean WTP figures than their female counterparts.


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Age: The means for the different variables were found to have small variances with the 30–45 and 60–75 year age groups having the highest SPP and MWTP figures whilst the dependent (15–30 and 75+ year) age groups had the lowest values. ANOVA tests showed that the SPP and MWTP for a new deep well were affected by age. The KruskalWallis test showed that the SPP for a new water source, as well as the SPP and MWTP for the repair of a borehole, were different for

Table 6. Comparison of respondents’ MWTP for treated water. Treated water—MWTP range (Z$/bucket—25 litre container) Source of 0 1–20 21–40 41–100 >100 water Shallow well Deep well Borehole River Dam Piped scheme Canals & water taps

6.7 32.9

2.5

1.3

0.4

5.4 4.6 7.1 5.9 2.9

2.1 3.7 0.8 0.8 5.1

1.7 2.5 2.1 2.1 9.2

0.4 1.3 0.4 0.4 2.4

0

0.4

0

22.1 32.5 20.6 19.8 44.7

0.4 2.5

Table 7. Comparison of respondents’ MWTP for untreated water. Untreated water—MWTP range (Z$/bucket—25 litre container) Source of 0 1–20 21–40 41–100 >100 water Shallow 9.2 32.5 well Deep well 6.7 23.4 Borehole 5 34.2 River 8.8 18.4 Dam 7.1 19.2 Piped 5.4 45.5 scheme Canals & 0.4 2.1 water taps

0.8

0.4

0

1.7 1.7 0.8 0 3.7

2.1 0.8 0.4 0.8 7.8

0.4 1.7 0 0.4 1.2

0

0.4

0

respondents with the different ages. It can therefore be concluded that age affected these variables particularly the 15–30 and 75+ year age groups. Occupation: Traditional leaders’ MWTP was Z$1 for borehole water, Z$5 for piped water and Z$0 for all the other water points as well as for all repairs. Communal farmers,


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local government officials and students had higher SPP/MWTP figures for most variables in decreasing intensity than traditional leaders, Agritex and ZINWA officials. ANOVA tests revealed that the SPP and MWTP for establishing a new deep well, SPP and MWTP for a new borehole, SPP and MWTP for repairing a borehole, and SPP and MWTP for repairing a broken down piped scheme, had significant variances due to occupation of the respondent. There was minimal negative association between occupation and the SPP and MWTP for a new water source, SPP and MWTP for a new borehole, SPP and MWTP for a new deep well, and the SPP and MWTP for borehole repairs. The SPP and MWTP for establishing a new deep well, SPP and MWTP for a new borehole, SPP and MWTP for repairing a borehole and SPP and MWTP for repairing a broken down piped scheme were shown to be significantly affected by occupation according to the Kruskal-Wallis test. Occupation had a weak association with these variables. This could be explained by the fact that more respondents did not have a stable income hence their responses masked those of respondents with stable sources of income. Access to piped water: The Levene test for equality of variances on the impact of access to piped water on respondents’ SPP/MWTP showed that there was homogenous variance, which implied that access to piped water did not affect differences in the SPP/MWTP. However, the Mann-Whitney test showed that access to piped water affected WTP for all water sources although respondents with piped water had lower SPP/MWTP figures compared to those without piped water except for borehole water. In order to establish whether demand for a better water service delivery existed in the communities, respondents were further asked whether they were willing to contribute towards the establishment of a new water source that would save women time compared to an old source, new borehole and deep well. Investment in a new water source for women’s needs: Respondents’ SPP and MWTP were not much different for a new water source that would save women time compared to an old source across the seasons. However, during drought the SPP/MWTP figures were higher than in winter and summer. The Levene test showed that variances in the SPP and MWTP values observed were due to the effect of the amount of rainfall received. Parameter estimates showed that Chitakatira had lower SPP and MWTP values than Nyanyadzi. Agritex/ZINWA officials, traditional leaders and local government officials had a decreasing effect that is lower SPP and MWTP values compared to communal farmers and students. Gender did not affect the respondents’ SPP and MWTP values although males had higher SPP and MWTP figures than females. The Mann-Whitney test showed that access to piped water affected the SPP/MWTP. Respondents with piped water had higher SPP/MWTP than their counterparts without. For the establishment of a new borehole, Chitakatira had lower WTP figures compared to Nyanyadzi, which decreased the SPP and MWTP values. Traditional leaders had lowest WTP figures whilst the Agritex/ZINWA officials had the highest SPP and MWTP figures. Drought had higher SPP and MWTP values followed by winter then summer. In this case females were found to have higher SPP and MWTP values than males. Access to piped water was shown not to affect respondents’ SPP/MWTP for establishing a new borehole. Occupation, age and region had significant effects on the SPP and MWTP for the establishment of a new deep well. Traditional leaders still had a decreasing effect on the SPP and MWTP whilst students had the highest SPP and MWTP values. The 15–30 year


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age group had the lowest SPP and MWTP values. Chitakatira had lower WTP values than Nyanyadzi, which lowered the SPP and MWTP values. Gender did not significantly affect the SPP/MWTP values although males had higher SPP and MWTP values than their female counterparts. Season did not have a significant effect on the SPP and MWTP values for the establishment of a new deep well. 4 DISCUSSION The evidence gathered in this study showed interesting perceptions held by rural people in relation to WTP for clean and safe domestic water. At a general level it can be said that there is no substance in the assertion that poor people do not want to pay for water. In Zimbabwe poor people have already begun to meet operational and maintenance costs in domestic water sources (Machingambi and Manzungu, 2003), and in publicly owned irrigation schemes, contrary to claims that the government maintained these schemes (Manzungu, 1999). Worldwide it has been documented that poor people tend to pay the highest amounts for domestic water (Cosgrove and Rijsberman, 2000). Where payments are not forthcoming the problem may be a lack of money rather than willingness to pay (Machingambi and Manzungu, 2003). Poor community mobilisation methodologies may also be another reason (Global Water Partnership, 2000). The study has also provided insights into specific issues concerning the supply of domestic water in rural areas, which may be of interest to policymakers and practitioners. It was clear that there was a high awareness of the potential danger caused by consumption of water containing bacteria. Respondents characterised clean and safe water as being free of bacteria. There was also a realisation of the likely causes of the contamination. This was shown by the fact that water was perceived to be generally unsafe in the wet season (hence lower WTP figures than for the dry season). Piped water had the highest WTP figures as it was rated the safest. River water was rated the most unsafe; it had the largest proportion of respondents not willing to pay anything for it in summer. Treating water had the effect of increasing MWTP figures. In some cases physical scarcity of water also affected SPP and MWTP. This explains why Nyanyadzi, the drier of the two regions, had respondents who were willing to pay higher amounts of money for their water than their counterparts in Chitakatira. The impact of physical scarcity of water on shaping the management of water resources is increasingly being acknowledged internationally. It is not absolute scarcity of water that is a problem but an economic scarcity regarding the availability of finances for the development and management of water resources (IWMI, 2000). This explains the paradox of a country like Zambia with more water resources than South Africa, but has a greater percentage of the population suffering from water scarcity more than the latter. Some commentators have also argued that water scarcity can lead to better adaptive capacities, which may mean the adoption of more intensive water uses (Turton and Ohlsson, 1999). This underlines the importance of analysing the role of social, cultural and economic factors in influencing willingness to pay for water. Socio-economic and cultural factors affected respondents’ WTP for water. The effect of the respondents’ economic circumstances on WTP for water was illustrated by the fact that economically dependent individuals’ (15–30 and the 75+ year age groups) were not


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interested in contributing towards their water use. Their WTP was not affected by whether the water was safe or unsafe since they showed no interest in paying for water. Generally traditional leaders were not willing to pay for water because they considered themselves as owners of the water, underlining the role of cultural factors in influencing the demand for water. Perceptions about who owns water also affected WTP (Machingambi and Manzungu, 2003). However safety was a fundamental factor in influencing respondents WTP as even the traditional leaders who were unwilling to pay for water from any other water source wanted to pay for the “safe” piped water. Females were found to have lower WTP than males probably due to the fact that they normally do not handle finances in the home. They therefore tended to be more conservative regarding money issues than the males. However females had low WTP figures in relation to investing in new water sources to reduce labour upon women. The influence of physical, socio-economic and cultural factors on the WTP provided a basis for respondents to portray their degree of concern about access to reliable, safe and clean water, the ideal institutional context in which water could be provided and the way in which it would be financed. Addressing such issues constitutes a more holistic intervention in water issues affecting respondents, rather than merely focusing on cost recovery. 5 CONCLUSION Demographic characteristics of respondents are important in influencing WTP for clean and safe domestic water. Cost recovery policies should therefore be related to demographic characteristics of the intended beneficiaries. While demand for reliable, accessible, clean and safe water was shown to exist in rural areas, success of cost recovery policies depends on the ability to pay. ACKNOWLEDGEMENTS The authors wish to thank the Water Research Fund for Southern Africa (WARFSA) for providing the grant that made the study possible. Mr Chimedza of the University of Zimbabwe’s Department of Statistics is greatly acknowledged for the assistance with data entry and analysis. REFERENCES CSO, 1992. Central Statistics Office, Census 1992, Provincial Profile: Manicaland. Government Printers. Chenje, M. & Johnson, P. (eds.) 1996. Water in Southern Africa, SADC/IUCN/SARDC. Harare, Print Holdings. Cosgrove, W.J. & Rijsberman, F.R. 2000. World Water Vision: Making Water Everybody’s Business. London. Earthscan Publications Ltd. Global Water Partnership, 2000. Towards Water Security: A framework for Action. GWP, Stockholm.


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Government of Zimbabwe, 1995. Poverty Assessment Study, Harare, Government Printers. International Water Management Institute, 2000. World Water Supply and Demand: 1995 to 2025. DTP Unit, IWMI—January 2000, Colombo. Machingambi, M. & Manzungu, E. 2003. An evaluation of rural communities’ water use patterns and preparedness to manage domestic water sources in Zimbabwe. Physics and Chemistry of the Earth: Water Demand Management for Sustainable Use of Water Resources, 28(20–27):1039– 1046. Pergamon Press. Makumbe, J.Mw, 1996. Participatory development: the case of Zimbabwe. Harare, University of Zimbabwe Publications. Manzungu, E. 1999. Strategies for smallholder irrigation management in Zimbabwe. PhD Thesis, Wageningen University, The Netherlands. Manzungu, E. 2001. A lost opportunity: The case of the water reform debate in the fourth parliament of Zimbabwe. Zambezia, XXVIII (i):97–119. Moyo, N.A.G. & Mtetwa, S. 2000. Water Quality Management Strategy for Zimbabwe. A paper prepared for the Ministry of Environment and Tourism, Harare. National Action Committee, 1997. Sustainability strategy for the National Rural Water Supply and Sanitation Programme, Government of Zimbabwe, Harare. Pearce, D., Markandya, A. & Barbier, E.B. 1989. Blueprint for a green economy. London, Earthscan Publications. Savenije, H. & van der Zaag, P. 2002. Water as an economic good and demand management: paradigms with pitfalls. Water International, 27(1):98–104. Turton, A.R. & Ohlsson, L. 1999. Water scarcity and social adaptive capacity: Towards an understanding of the social dynamics of managing water scarcity in developing countries. Paper presented at the Workshop on Water and Social Stability at the 9th Stockholm Water Symposium on Urban Stability through Integrated Water-Related Management, hosted Stockholm Water Institute (SIWI), Stockholm, Sweden, 9–12 August. www.soas.ac.uk/Geography/WaterIssues/OccasionalPapers/home.html Vincent, V. & Thomas, R.G. 1960. An agricultural survey of Southern Rhodesia: Part I—agroecological survey. Salisbury, Government Printer.

The role of supplementary irrigation for food production in a semi-arid country—Palestine Mohammed Yousef Sbeih Irrigation Project Coordinator, American Near East Refugee Aid (ANERA), Ramallah, West Bank, Palestine Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: Palestine consists of the West Bank and the Gaza Strip. The proclaimed state of Palestine has a land area of 6657km2. Water is considered an essential factor of life and needs to be developed in arid countries. Reuse of treated wastewater for irrigation as supplementary irrigation will increase the irrigated area in Palestine and replace fresh water.

1 INTRODUCTION Palestine consists of the West Bank and the Gaza Strip. The proclaimed state of Palestine has a land area of 6657km2. Water is always considered as an essential factor of life and development in arid and semi-arid countries. In Palestine the total per capita water consumption is 139m3. The total available water for Irrigation is 239 M.C.M. which is responsible for irrigating only 330000 dunums out of 2314.000 dunums cultivated that can be irrigated if water is available i.e. 5% of the total cultivated land. The average rainfall is 450mm and unfortunately there isn’t any water harvesting structures i.e. dams, most of this rainwater flowing towards the Dead Sea or the Mediterranean Sea as waste. So harvesting this water in individual farmer land and using this water for supplementary irrigation to irrigate olive trees, almonds, grapes and cereals will be of a great impact on the Palestinian land for feed production. It should be noted that there are few farmers who practice supplementary irrigation for production of vegetables that are planted in summer as individual initiative. The quantity and quality of production that they have is extremely tangible. Since most of the land in Palestine is planted by olive, grape, and cereals, supplementary irrigation should be introduced and practiced where the production of wheat via irrigation by treated wastewater was three times that under rain fed planting project implemented in a pilot project.

The role of supplementary irrigation for food production in a semi-arid country-Palestine

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Reuse of treated wastewater for irrigation as supplementary irrigation will increase the irrigated area in Palestine and will replace the fresh water that can be used for domestic purposes. 2 THE NEED FOR SUPPLEMENTARY IRRIGATION IN PALESTINE As it was mentioned before, Palestine is a semi-arid country, where the average rainfall is 450mm. The availability of water is questionable. Furthermore, the availability of water for agriculture is reducing in a tangible way due to the following: 1. The normal increase in growth rate, the population of the country is increasing, so the demand for domestic water is also increasing. This will affect the availability of water for agriculture. 2. Since rainwater is the only source of water, the quantity of rainwater (rainfall) has been decreasing in the recent years. 3. There is a huge conflict on water issues at this stage between the Palestinians and the Israelis since Israel occupied Palestine. It should be mentioned here that during early negotiations in the peace process, four main issues have been delayed since 1992; they are Jerusalem, refugees, water and borders. Still after 8 years of negotiations, there hasn’t been any significant movement on these issues. So the quantity of water that can be available for the Palestinians will probably not be increased. 4. The quality of ground water wells especially in Gaza and Jericho becomes saline and shortly it cannot be safely available for agriculture. From the above, it seems that extra availability of water for additional irrigated area or even to sustain the irrigated area is not an easy task. Total cultivated area in the West Bank is 2100.00 dunums, but the irrigated area is 110000 dunums. From the small experience (pilot project) for this field as well as other country experience i.e. Syria. It has been proven that the production of crops under supplementary irrigation is 3 times higher than under rain fed crop, in addition to the increase in the quality of the product. So if supplementary irrigation has been practiced we can easily increase the production of rained crops to three times or twice. This will play a major role in providing food for the people and even exports can take place and the net income of the country will be increased. 3 BACKGROUND It is foreseen that the world’s food production has to be doubled in the next 25 years, and thus, the agriculture continues to be an important sector in the 21st century. Meanwhile, the agriculture sector remains the largest user of the water resources, and it is evident that there is a decline of agricultural water due to increasing demands from cities, industries, and hydropower utilities in the developing countries such as Asia. Much of the water has to come from irrigation water savings.


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Population and economic growth in many developing countries of Asia have created serious problems, such as the shortage of food, the scarcity of water, and the deterioration of the environment. Some of the irrigation and drainage projects have been seriously criticized due to their high-cost and low-efficiency for the construction and maintenance. The concept of maximum yield is now changing to optimum yield for creating an efficient irrigation schedule. The water saving is the most sustainable conservation, because it reduces the new construction needs to meet the increased water demand. The major issues of agricultural water are how to increase withdrawals about 15–20% by water saving, how to increase storages 10–15% by new irrigation facilities, and how to conserve the water quality of irrigation. 4 SUPPLEMENTAL IRRIGATION 4.1 Definition ICARDA defines supplemental irrigation (SI) as; the addition of essentially rain fed crops of small amounts of water during times when rainfall fails to provide sufficient moisture for normal plant growth, in order to improve and stabilize yields. Accordingly, the concept of SI in areas having limited water resources is built on three bases: First: water is applied to rain fed crops, that would normally produce some yield without irrigation; Second: since precipitation is the principal source of moisture for rain fed crops, SI is only applied when precipitation fails to provide essential moisture for improved and stabilized production and; Third: the amount and timing of SI are not meant to provide moisture stress-free conditions rather to provide minimum water during the critical stages of crop growth to ensure optimal instead of maximum yield. The management of supplemental irrigation is seen as a reverse case of full or conventional irrigation (FI). In the latter the principal source of moisture is the fully controlled irrigation water, while the highly variable limited precipitation is only supplementary. Unlike FI the management of SI is dependent on the precipitation as a basic source of water for crops grown. Water resources for supplemental irrigation are mainly surface, but shallow ground water aquifers are being increasingly used lately. Non-conventional water resources are of a potential for the future, but an important one emerging is water harvesting (Dwas 2001). 4.2 Improving production with SI Research results from ICARDA and other institutions in the dry areas as well as harvest from farmers showed substantial increases in crop yields in response to the application of relatively small amounts of supplemental irrigation. This increase covers cases with low as well as high rainfall. Average increases in wheat grain yield under low, medium and high annual rainfall in Tel Hadya reached about 400%, 150% and 30% using amounts of


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SI of about 180, 125 and 75mm respectively. Generally, optimal SI amounts range from 75mm to 250mm in areas with annual rainfall between 500 to 250mm, respectively. Determining the optimal amount under various conditions will be discussed later (Oweis 2001). When rainfall is low, more water is needed but the response is greater, but increases in yield are remarkable even when rainfall is as high as 500mm. The response was found to be higher when rain distribution over the season is poor. However, in all rain fed areas of the region it was found that some time in the spring there is usually a period of stress, which threatens, yield levels. This soil moisture stress usually starts in March, April of May, if total annual rainfall received is low, average or high respectively (Oweis 2001). In Syria average wheat yields under rain fed conditions are only 1.25t/ha and this is one of the highest in the region. With SI the average grain yield was up to 3t/ha. In 1996 over 40% of rain fed areas were under SI and over half of the 4 mil tons national production was attributed to this practice. Supplemental irrigation does not only increase yield but also stabilizes farmer’s production. The coefficient of variation in rain fed production in Syria was reduced from 100% to 10$ when SI was practices. This is of special socio-economic importance since it affects farmer’s income (Oweis 2001). 4.2.1 Introduction Historical Palestine is located between the Mediterranean Sea and the Jordan River, as well as to the Red Sea from the south. The present proposed Palestinian state consists of West Bank and Gaza Strip. The other part of Palestine is occupied by Israel in 1948. This study focuses on the West Bank and the Gaza Strip. The proclaimed state of Palestine has a land area of 6657 square kilometres (Kateeb 1993). Population senses has been taken place recently by the Bureau of Statistics early 1998. It is reported that the population of the West Bank is 1571571 and Gaza Strip is 963026 where the total population of the Palestinian people is 2534598 people. Ground water is the main water source in the country. It is recharged by rainfall. Rainfall varies from 100mm in the south east to 800mm in the north. The average rainfall is 550mm (Sbeih 1995). Where the average rainfall in Jordan Valley is from 100mm to 270mm/year (Zaru 1992), and in Gaza is 200–400mm/year (Abu Safieh 1991). Not all the rainwater is available to the Palestinian due to Israeli Military orders. Water is abstracted from the ground water through 340 wells in the West Bank and 1781 wells in Gaza. In addition to that springs contribute a lot, where half of the irrigation water in the West Bank is due to springs. The quality of the available water varies from almost rain water to brackish water. In the Jordan Valley where it is the lowest point in the elevation in the world where temperature is very high in this area especially in summer. As example, the chloride content is reaching 68mg/l and the SAR reaches 11.7 where the TDS reaches 5000PPM. Still the utilization of this saline water is not as efficient and environmentally safe as it should be where further utilization of this water could play a major role in developing the area where still the irrigated area consists of not more than 6% of the cultivated area in the West Bank.


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It should be mentioned that not only saline water does already exist and utilized unproperly, but it also seems to be that the additional water that can be allocated for irrigation is also saline water which is going to be from: 1. The Eastern aquifer to be used in Jordan Valley. 2. From the treated waste water from different cities and villages in the West Bank. 4.2.2 Water sources in occupied Palestine 4.2.2.1 West Bank Two main water sources are available for Palestinian in the occupied Palestine (West Bank and Gaza Strip) for agricultural, domestic and industrial use. These are rainfalls and ground water sources—Palestinians consume water mainly through ground water wells and springs (where rainfall is considered the main recharge). The total annual water springs discharge varies according to the rainfall. The total annual flow of the 113 fresh water springs in the West Bank ranges between 24 M.C.M. (as in the year 1978/79) to 119.9 M.C.M. (as in the year 199/92) and with an average of 52.9 M.C.M. as calculated from the annual flow in the past 24 years. Around 86% of the total annual flow of these 113 springs is within the eastern drainage (in/or toward the Jordan Valley), while the other 14% is within the western and south-west (Nusseibeh 1995) where the total estimated annual water discharge from ground wells is 60 M.C.M. (Awartani 1992). So that the total annual water available to Palestinian is 113 M.C.M. In addition to that there is another 2.5 M.C.M. is collected directly from the rainfall in cisterns in Palestinian houses. So that the total available water is 116 M.C.M./year, for more information see Table 1. 4.2.2.2 Gaza Strip Water situation in Gaza Strip is very critical. The Gaza Strip lies on top of two water strata. The upper is fresh water, the lower carries saline water. The annual consumption of water is at present in the vicinity of 100 M.C.M. These aquifers get replenishment of some 60% leaving a deficit of 40 M.C.M. of water (Shawwa 1991). Even the Gaza water is lower in quality than West Bank, but due to the complication of the situation there and due to the geographic location where my work is more in the West Bank. This paper will address West Bank issues more clearly.

Table 1. Basic land and water indicators for Israel and the occupied Palestinian and other Arab territories. West Bank

Gaza Strip

Israel

Total area 5573000 360000 20000000 (dunums) Population (1988) 900000 600000 4300000


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Area of land 2100000 214000 4250000 cultivated (dunums) Area of land 110000 120000 850000 irrigated (dunums) Percentage of total 5 56 44 irrigated land (%) Percentage of total 38 59 21 land cultivated (%) 95 80 1320 Annual water consumption for irrigation (million m3) 27 21 325 Annual water consumption for households (million m3) 3 2 125 Annual water consumption for industry (million m3) Total annual water 125 103 1770 consumption (million m3) Total per capita 139 172 411 water consumption (m3) 35 75 Per capita water 30 consumption per household (m3) Per capita water 3.3 3.3 29 consumption for industry (m3) Per capita water 106 133 307 consumption for irrigation (m3) 1 dunum=1000m2. Source: Israeli land and water policies and practices in the occupied Palestinian and Arab territories, unpublished study in Arabic (Economic and Social Commission for Western Asia, Baghdad, 1990), p. 8.

4.2.3 Irrigated areas in the occupied Palestine In Palestine, being a semi arid country, we are confronted by a demographic growth, and agricultural development as well livestock and industrial development. Thus in essential growing water requirement makes the rational management of water resources supremely important in order for development to be lasting and for environment to be served.


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On a global basis at least 60% of all water abstracted at present is used for agricultural production. In Palestine 70% of all water consumed is due to agriculture. Here in Palestine, agriculture is considered to be one of the main national income. Agricultural production contributes 47.61% of the total national income in 1970. The potential for irrigation to raise both agricultural productivity and the living standards of the rural poor has long been recognized. Irrigated agriculture occupies approximately 17% of the world’s total available land but the production from this land comprises about 34% of the world total. In Palestine, irrigation is considered to be the spinal chord of plant production for the following reasons: 1. Palestine is considered as a semi arid region where some of the crops cannot be grown without irrigation (example, citrus). 2. In the Jordan Valley, which constitutes the main agricultural production for the country, irrigation is a must due to low rainfall and high temperature. 3. With irrigation the same plot of land can be planted up to three times per year while it cannot be planted more than two times with dry farming. 4. Different varieties and crops can be planted in any region due to the availability of water i.e. more flexibility of planting several crops at different regions in different times of the year. 5. Job creation: Since the labour requirement per irrigated dunum is more than double that of job required per dry farming per one season. This has now become more vital due to continuous of closures of the West Bank and Gaza Strip where the number of labourers that are working in the Palestinian part that occupied in 1948 is sharply reduced. 6. Agricultural production is much higher for irrigated farming than for dry farming per dunum per season. As example average tomato production per dunum is as follows: – Dry farming: 2–3 ton per dunum per season. – Irrigated (open land) 6–8 ton per dunum per season – Irrigated (greenhouse) 12–16 ton per dunum per season 7. Net income per dunum of dry farming does not exceed $150 while from irrigated area the net income can exceed $1500 per dunum. 8. Especially in Palestine, where the horizontal expansion in agriculture by increasing the total cultivated area due to the Israeli occupation, and shortage of water. The vertical expansion could be the main parameter to play with. Irrigation will be the main element in this formula. So that providing extra water for irrigation to irrigate as much as possible of the cultivated area is a must. This implies that Palestinian should use any drop of water. Regardless the quality of that water practically and efficiently: Table 2 shows the irrigated area in each district in Palestine where the total irrigated area in 1993–94 was 217000 dunum (PSBS 1996).


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Table 2. Distribution of area that could be irrigated in the West Bank (Source: Awartani, 1991). Location

Dunum

Plains in Jenin and Tulkarem Highland Eastern slopes Jordan Valley Total

99600 27740 64.6 93.5 535.1

4.2.4 Available area that is ready for irrigation Where in Gaza Strip the irrigated area could be doubled or tripled in terms of topographical situation but due to the limitation of the water both quality and quantity it is very difficult to increase the irrigated area while in the West Bank the area that could be irrigated in terms of topographical conditions estimated to be 535 thousand dunums (Awartani 1991) as in Table 2. Where in the study conducted by PWA in 1992 in order to develop a plan for the western Ghore the following locations could be the most suitable area to be ready for irrigation. 4.2.4.1 Northern Ghore The areas suitable for irrigated agriculture in this region include: 18000 dunums in Ein Al Beida, Bardalla villages 5300 dunums in the Ghore 3500 dunums in the Ghore But the Ghore and Zhor areas are mostly closed by the Israeli Military orders. 4.2.4.2 El-Bique Valley This is a large flat area to the west of the hills of northern Ghore. This area includes about 18500 dunums of fertile smooth deep soil. The Palestinian farmers as rainfed excluding 5500 dunums where the two settlements their (Baquat and Roi) are occupying cultivate all this area. 4.2.4.3 Upper El Fara’ Valley area (Semi-Ghore) In this area, there are 13100 dunums that are suitable for irrigation and can be easily irrigated as follows: Sahl Tubas Sahel Tayassear Sahel Tammun Sahel El Fara’ El Nassarieh (additional)

3600 dunums 900 dunums 1900 dunums 5000 dunums 1700 dunums


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Where there are another 7000 dunums, which are already irrigated. 4.2.4.4 The middle and south Ghore This region extends from approximately grid north 180 (northern of Marj Najeh) in the north to the Dead Sea in the south and from the Jordan River in the east to the feet of the west-bank mountains. The total area that could be ready for irrigation in this area is 145500 dunums. In summary, the total area that can be used in irrigated agriculture in the western Ghore will be: Northern Ghore Biquia Valley Semi-Ghore Southern Ghore Total

26800 dunums 18500 dunums 201000 dunums 145500 dunums 210900 dunums

Where about 44000 (PCBC 1991) dunums of this area is currently irrigated. So the total additional area that could be irrigated in the West Bank is (210900−44 000+(535100−935000)= 608500 dunums. It should be mentioned that the Jordan Valley produces more than 59% of the vegetables produced in the West Bank. It also produces 100% of the bananas produced in Palestine. 5 PALESTINIAN EXPERIENCE OF SUPPLEMENTARY IRRIGATION Still the term supplementary irrigation is not even used formally and officially in Palestine. Until this time there is not any plan of implementing any project of supplementary irrigation. This is mainly due to the lack of qualified staff at the Ministry of Agriculture as well as to the lack of great interest to agriculture from M.O.A. due to the following reasons: 1. The lack of responsibility of the Palestinian Authority on most of the agricultural land due to the occupation. 2. The lack of finance and funding to development projects. Nevertheless, there are individuals who attempt to use supplementary irrigation, an example of that are few farmers in Sinjel town in the Ramallah area. 6 DESCRIPTION OF AGRICULTURAL AREA IN SINJEL This village is located just between Ramallah and Nablus cities, situated 20km to the north of Ramallah. The total agricultural area in the village excess 4000 dunums, out of these areas. About 1000 dunums are plain and flat.


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This 1000 dunums is planted with vegetables in summer and cereals in winter. All of this area is rain fed, there are no source of water for irrigation since this area is located close to the village (houses), it is easy for the farmers to bring water by mobile tanks. Usually the farmers in summer, bring some water and store them in a container (barrel) of 200 liter capacity each, since the ownership of land is between 3–5dunums, the number of barrels used are 6–8. In summer farmers used to plant vegetables, at the time of planting the seedlings, farmers used to irrigate the seedling by a bucket. Farmers used to mix the fertilizer water and irrigation at the time of planting the seedlings. Later on, after 20 days the second irrigation with fertilizer is applied. The third one and the last one are provided with fertilizer before flowering. The total amount of water applied per each plant is not more than 1 liter, for a dunum of 1000 plants, 1000 liter is applied 1 cubic meter of water applied for the whole season per one dunum. While for the irrigated area the minimum irrigation water requirement is 70m3/dunum per the season. In this village, Sinjel, and through my investigation, in the year 2000 I found 3 farmers who are using this approach technology, when I asked one of them what is the result that you will expect, he broadly replied: 1. The quality of agricultural product that I used to obtain for the last two years where I used to use supplementary irrigation is much better than the product of my neighbor in the same plot of land in the village, so the price per 1kg. That I got is much higher also. 2. The total production is much higher than that of my neighbor, i.e. I got 4 tons each per dunum, my neighbor got 2 tons of squash per dunum. 3. The period of production that I have is much bigger than that of my neighbor has, this means that total income that I gained is much higher. I used the produce vegetables for 2 months, while my neighbor only one month, i.e. the harvesting period is much higher when supplementary irrigation used. I informed this farmer that I am working on an irrigation project coordinator for an NGO that provides funds for farmers. Since this farmer believes that he was happy from his production since he has only 3dunums and all of his family working in this plot of land, he did not ask what service that since that we offered, this totally indicated that he is happy, and he did not need any further assistance. At that time there was visiting irrigation professor from Canada. This professor told me that we should use him as a model to encourage people using appropriate technology. Another example of using supplementary irrigation is found in Hebron where a farmer from Al Tamimi family, who has a grape field and luckily a pipe water pass through his field and used to get some water from this pipe and provide some water for his grape. In winter since the rainfall in Hebron is not exceeding 300mm, as well as in July.


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Table 3. Results of El Bireh wastewater treatment pilot plant using treated wastewater. Treatment

Production of wheat (anber variety), all the plants (kg/dunum)

Irrigation with treated wastewater with fertilizer Irrigation with treated wastewater without fertlizer Without irrigation, with fertilizer Without irrigation, without fertilizer

2520

20036

1600 572

It is well known in Hebron, that the quality of grape of that man is the best in Hebron, since Hebron is of the biggest producing city (country) in Palestine. Since the municipality constructed a pilot treatment plant, it thought of planting crops using the treated effluent. This was funded by American Near East Refugee Aid (ANERA). Three crops were selected by the Agriculture Department to be planted for the first time in Palestine using treated wastewater: ● Artichokes on 150m2—planted on October 31, 1993. ● Onion frozen production on 500m2—planted on November 6, 1993. ● Wheat on 1000m2—planted on November 22, 1993. ● Drip irrigation as well as sprayers were used. Several treatments were made as follows: ● Irrigation with wastewater used, fertilization was used. ● Same as above, but without application of fertilization. ● Irrigation not used but fertilization was used. ● No irrigation and no fertilization (dry land farming). All the agricultural practices were used (pesticides, ploughing, seed control, etc. Table 3 shows the production of each kind of treatment. The impact of using treated wastewater appears clear. Notes: 1. Time of planting was October 1993; all the crops received rainfall during the growing period. 2. Time of harvesting was June 2, 1994. 3. Production with irrigation with treated wastewater with fertilization was five times without irrigation and fertilization. 4. Production increased the soil when irrigated with treated wastewater where fertilization was applied on both cases (irrigated and non-irrigated).


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7 METHODOLOGY OF PRACTISING SUPPLEMENTARY IRRIGATION IN PALESTINE Since the ownership of land is very small in size i.e. from 5–10 dunums, supplementary irrigation can be easily implemented for vegetables, trees and to cereals to some extent constructing of small ponds of 40–50m3 capacity, i.e. this pond can be located on a 14–18 meter square area. This pond can be located on the lowest point in elevation of the individual land. This land serves two farmers if agreed upon where it can be sited on the border of each farmer land. Distributing of water to the plant can be done manually by lifting the water and distributing it to the plants by a bucket. Another way of distributing this water that this water can be lifted manually from the pond and poured into a barrel that can be located on the dip of the pond with 1/2meter raised over the surface so water can be distributed to the plant by gravity through pipe line. The farmer can distribute the water pipe from the plant to another. These methods can be implemented

Table 4. Results of Al Beireh Pilot Wastewater Treatment, 1994.

Crop Wheat 870 type

Kind of treatment

Production (kg/dunum) Seed Hay

Irrigation with 687.5 fertilizer Irrigation 656.70 without fertilizer Rainfed with Rainfed with 537.5 fertilizer fertilizer Rainfed without 500 fertilizer Wheat anber Irrigation with 864 type fertilizer Irrigation 824 without fertilizer Fertilizer Rainfed with 600 fertilizer Rainfed without 236 fertilizer

1375 1373

1187.5 1531.25 1656 1212

1000 336

easily with zero operation cost. Since only the farmer himself can conduct this job easily, another method of distributing water is by using a small pumped electricity is available since the head required is very small. In the case of cereals water can be distributed easily by establishing ponds, so water can be discharged into the farm then water can flow by gravity. In order to reduce the


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cost of pumping farms can cooperate between themselves when each farmer can construct his pond on the highest point in elevation on his land. His pond can receive water from his neighbour’s field and so on. 8 THE ECONOMY OF SUPPLEMENTARY To construct a pond of 50m3 the following is needed with estimated costs: 1. 2. 3. 4.

Excavation of 50m3 Construction works Plastering Parallel, pipes, buckets Total estimatated cost:

=$3900 =$2000 =$500 =$120 =$3100

9 REVENUES Assume a plot of land of 5 dunums planted with vegetables. The production of vegetables of rainfed per dunum is 3 tons/dunum, the production of dunum with supplementary irrigation is 4.1 ton. The price per ton is $200 for rainfed crops.

The income per supplementary irrigation is 4×250=$1000.

The price per ton for supplementary irrigation is $250.

The net income due to supplementary irrigation will be 1000?=400 per dunum.

S the income per rainfed dunum=3×200=$600.

5 dunums×400=2000 per session per 5 dunums.

10 CONCLUSION AND RECOMMENDATIONS 1. In Palestine the total cultivated area is 2314000 dunums, while the irrigated area is 230000 dunums, so any efforts for increasing the productivity of the cultivated area should be considered due to the large area, while the production of the irrigated area is on its maximum. 2. Providing of extra water or even to sustain the existing water for both irrigation and domestic purposes is questionable due to the increase demand for domestic purposes first and due to the Palestinian-Israeli water conflict. 3. Practicing supplementary irrigation is not costly and did not need that much complicated technology. 4. The irrigated area only represents 6% of the cultivated area, where the land that can be easily irrigated is estimated to be 608600 dunums. In the West Bank only, which is 6 times the land that is already irrigated but water is needed. 5. The salinity of the ground water is deteriorated by time due to over pumping, sea intrusion and the low rainfall especially in the Jordan Valley and in the Gaza Strip, so providing fresh water for irrigation is questionable.


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6. The additional water that will be available for the Palestinians will be either from (a) Eastern aquifer, (b) Jordan River, or (c) Treated wastewater. Where all of this water is saline water, where there are another source such as the mountain aquifers, but this seems to be difficult to be secured soon. 7. The early possible of expansion in irrigation will be in Jordan Valley where the existing water wells and the future water that might be available is saline. 8. Since the treated water is in the full control of the Palestinians, more attention and care should be paid in order to better and safe utilize of this water for developing the agricultural sector in Palestine, and this water can be used for supplementary irrigation. 9. The productivity of one cubic meter of water with supplementary irrigation is much higher than that of irrigated land since the water prepared by irrigated dunum is 7 times more than the required for supplementary irrigation. 10. The existing irrigated area is already exhausted since this land used to be planted two or three times a year where the other land used to be cultivated once a year even it kept fallow on some years. 11. Palestinian Agricultural Ministry and Palestinian Water Authority should recognize the situation and consider supplementary irrigation as a major element for food supply.

REFERENCES Abdul Jabar, Q. 1996. Chemical analysis of Jericho wells. PhD, Jerusalem. Abu Arafeh, A. 1894. Jordan Valley, Jerusalem, published by Arab Studies Society. Al Khateeb, N. Palestinian water supplies and demands. A proposal for the development of a required water master plan, IPC, Jerusalem. Awartani, H. 1991. Irrigated Agriculture in the Occupied Palestinian Territories, Al Najah National Univseristy, Nablus. Awartani, H. 1992. Groundwater wells in the Occupied Palestinian Territories, PhD, Jerusalem. ICID, 2001. General Report to the First Asian Regional Conference of International Commission on Irrigation and drainage. Agricultural, Water and Environment, Seoul, Korea. Nusseibeh, M. & Nasser Eddin, T. 1995. Palestinian Fresh Water Springs, Jerusalem, Palestine. Palestinian Water Authority, 1992, Water Development Plan, Jerusalem, Palestine. Sbeih, M. 1995. Recycling of treated wastewater in Palestine: Urgency, obstacles, and experience to date, Elsevier. Oweis, T. 2001. Supplemental Irrigation for field crops, water saving and increasing water productivity: challenges and options. University of Jordan, Amman, Jordan.

Conversion of priority water rights to proportional water permits and conflict management in the Mupfure river catchment, Zimbabwe Tamsanqa Mpala Scientific & Industrial Research & Development Center (SIRDC), Harare, Zimbabwe Water Resources of Arid Areas–Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: The Zimbabwe Water Act of 1976 was repealed and replaced by the Water Act of 1998. The Water Act of 1998 (Chapter 20:24) came into force on the 1st January 2000 and with it came the abolishment of the prior date system of water allocation. In the promulgation of the new Water Act, existing water rights used under the priority date system were to be converted to proportional water permits. The objective was to promote equitable access to water resources for all Zimbabweans and to encourage the sustainable utilization of the resource. The challenge for the newly established catchment councils was therefore to determine all existing water rights in their respective catchments and conduct the conversion exercise based on water generated in the catchment and water use by water right holders. This study analyzed the existing water rights and water generation for the Mswenzi River catchment and conducted the conversion to water permits with the Sanyati Catchment Manager.

1 INTRODUCTION Any resource, such as water, when used by more than one user in a single catchment or river basin, tends to attract conflicts about how it is shared and distributed. This paper focuses to a large extent on a highly committed small river catchment; namely, the Mswenzi River Catchment that forms part of a greater basin, which eventually drains off into the Zambezi River and into the Indian Ocean. The Mswenzi is a tributary of the Shuru Shuru River in the northwestern region of Zimbabwe. The Shuru Shuru River in turn is a tributary of the Mupfure River that drains northwesterly and into the Zambezi River. The study catchment has a total surface area of approximately

Conversion of priority water rights to proportional water permits and conflict management

255

158km2 with the Mswenzi River stretching a distance of 22km. The study catchment generates on average an estimated 70mm of surface water per year, or 11.0*106m3/year. Hence, this paper looks into the operationalization of water rights in the Mswenzi river catchment and gives an analytical recommendation of converting the old water rights used under the Zimbabwe Water Act (1976) to new water permits as recommended under the new Zimbabwe Water Act of 1998. A water right, for the purpose of this study, has been defined as a right to use beneficially a certain volume of water expressed in absolute volumetric units per time unit, whilst a water permit is a permit or allowance for the use of water, which specifies and restricts the use of water allocated. At the same time the paper attempts to bring out the conflicts involved in the Mswenzi catchment between upstream and downstream commercial water users. The paper discusses the legislative policies by looking at the old and new Water Acts and highlights the important principles that will govern conflict management and help spells out recommendations for water authorities and catchment management institutions. 2 THE WATER ACTS In Zimbabwe, the Water Act of 1976, which was repealed by the new Water Act of 1998, vested all public water in the President and private water was water belonging to the owner of land on which it was found. The right to use water was dependent on the type of use. For primary use no right was required. Access of water for non-primary use was based on the prior appropriation doctrine, where an appropriated right was based on the application of the appropriated public water to some beneficial use. The granting of any water right was the exclusive function of the Administrative Court sitting as the Water Court. The right would only be granted if public water was available and if it could be ascertained that the water would be put to beneficial use. The right granted was dependent on the date on which the application for the right was made. This date determined the applicant’s priority in the use of water applied for. The new Zimbabwe Water Act of 1998, which replaces the old Water Act (1976) sought to bring about equal and fair distribution of the available water resources in the national interest for the development of the rural, urban, industrial, mining and agricultural sectors. The major principles of the new Water Act were that all water would now be owned by the State and any use of it other than for purposes of primary use should be approved by the State. All stakeholders should be involved in decision-making processes and contribute to sustainable management of water resources. Water resources would be managed at catchment and sub-catchment levels, and the environment would also be considered a legitimate user of water. One of the important changes of the Water Act that is brought out in this study is that the priority date system of first come first served of water allocation was abolished to enable the principle of equitable access to water and sharing of water at all times. A fractional allocation system is now the recommended allocation system for non-primary water use.


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3 THE CONVERSION EXERCISE The Mswenzi River Catchment has an area of approximately 160km2, and on average generates 11.0*106m3/a of blue water. Water generated in the catchment is based on the annual unit runoff and the catchment area, where the water generated (m3/a), is a product of the two. Mean unit runoff for the catchment is 70mm/year and the calculated catchment area is 158.15km2. This gives an amount of 11.0*106m3/a as water generated in the catchment. The Mswenzi River catchment has a total of 17 existing water rights owned by mainly commercial farmers, who have built reservoirs with a total capacity of 7.3*106m3. Among the 17 water rights, the total commitment level of the catchment is 65%. This is water used, (m3/a) as a fraction of water generated (m3/a). The major dams in the catchment are Balwearie and Tawstock dams, which have a combined capacity of 4.9*106m3, and serve a total of 8 water rights to various farmers in the catchment. The other 9 water rights are served from smaller dams along the Mswenzi River. Table 1 shows existing water rights and current users in the catchment as well as the priority date for each property. The procedures for the conversion of water rights to water permits were that, (i) the priority date attached to each water right be removed, (ii) volumes of flow and storage rights as allocated in the old system remain the same and shall be used as permits until such a time as the water authorities see fit to amend or revise the permit, and that (iii) water rights be converted according to the applicants ability to beneficially use the water. In the conversion exercise a simple formula has been recommended for the purposes of the study catchment, which follows: Permit (m3/a), P=[S1+S2+S3…]+F1+F2… Where, S=storage (m3/a) abstraction from stored water. F=flow (m3/a) abstraction from river flow. The storage permit is the volume of water permitted to be stored and used while a flow permit is the volume of water, which can be abstracted and used directly from the river. The validity of the permits, is for a limited period of 20 years, thereafter they are reviewed.

Table 1. Review of existing water rights and current users in the Mswenzi catchment. Water Property right number 7573 8881

Kasama

River Priority Abstraction Abstraction Dam right from right from flow storage (103m3/a) (103m3/a)

Mswenzi 19/10/66 tributary Dodington Mswenzi 06/03/70 tributary

0

45 Weir

0

136 Farm dam


10626

12007

Rem. of Mswenzi 31/10/73 Luton Balwearie Mswenzi 31/05/73 Rem. of Mswenzi 05/10/83 Luton Balwearie Mswenzi 01/06/81 Balwearie Mswenzi 14/11/73 Strathspey Mswenzi 28/05/49 Strathspey Mswenzi 23/09/70 Strathspey Mswenzi 24/10/73 Handley Mswenzi 16/01/80 cross Cornucopia Mswenzi 24/10/73 Handley Mswenzi 24/10/73 cross Merchiston Mswenzi 28/01/81

14322

Merchiston Mswenzi 20/10/88

0

14321


0

12014


0

10156 10626 10156 10156 2276 2276 2276 12398 10364 9101

Total Source: Field notes, 2002.

0

910 Balwearie

0 0

1040 Balwearie 520 Balwearie

0 450 0 0 0 0

130 Balwearie Balwearie 400 Tawstock 182 Tawstock 518 Tawstock 1530 Suri Suri canal 523 Tawstock 714 Tawstock

0 0 0

450

257

611 Farm dam 20 Farm dam 5 Farm dam 20 Farm dam 7304

Balwearie Farm, which is served by Balwearie Dam, utilizes an estimated 1.59*106m3/a of water for its various crops under irrigation, hence the permit using the above formula will be: P=[1040*103m3/a+130*103m3/a] +450*103m3/a =1620*103m3/a for a validity of 20 years. Conversion for other properties in the catchment include: Kasama, P=[45*103m3/a] for a validity of 20 years. Dodington, P=[136*103m3/a] for a validity of 20 years. Rem. Of Luton, P=[910*103m3/a+520*103m3/a] =1430*103m3/a for a validity of 20 years. Strathspey, P=[(400+182+518)*103m3/a] =1100*103m3/a for a validity of 20


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years. Handley Cross, P=[2244*103m3/a] for a validity of 20 years. Cornucopia, P=[523*103m3/a] for a validity of 20 years. Merchiston, P=[(611+20+5+20)*103m3] =656*103m3 for a validity of 20 years. The new permits as recommended for the study catchment after the conversion exercise is shown in the Table 2. 4 CONFLICT MANAGEMENT IN THE UPSTREAM, DOWNSTREAM CASE The case singles out the dispute between upstream and downstream commercial farmers holding water rights in the Balwearie and Tawstock Dams where the latter is downstream. Downstream

Table 2. Water permits for Mswenzi river. Water Property permit number 7573 8881 10626 10156 2276 12398 10364 12007 Total

Kasama

River Abstraction permit (103m3/a)

Mswenzi tributary Dodington Mswenzi tributary Rem. of Mswenzi Luton Balwearie Mswenzi Strathspey Mswenzi Handley Mswenzi cross Cornucopia Mswenzi Merchiston Mswenzi

Dam

45 Weir

Validity 20 years

136 Farm dam

20 years

1430 Balwearie

20 years

1620 Balwearie 20 years 1100 Tawstock 20 years 2244 Suri 20 years Suri/Tawstock 523 Tawstock 20 years 656 Farm dam 7754

farmers who held earlier water right priorities in Tawstock Dam were outraged that they were not receiving sufficient water from upstream Balwearie Dam and as a result jeopardized their operations. As earlier applicants, Tawstock farmers were entitled to water first, which meant that Balwearie farmers had to open the outlet gates at Balwearie Dam and release water for Tawstock farmers before the former could store and use any water. In 1982 An investigation came about as a result of a submission for a decision made to the Administrative Court by Tawstock farmers who possessed water rights no, 2276,


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10364 and 9101 of Tawstock Dam and who are referred to as the applicants. The applicants were concerned that the holders of water rights no, 10156, 10626 and 10659 (Balwearie Farmers) of Balwearie Dam who are referred to as the respondents, were unable to pass sufficient water from their storage works to satisfy the downstream priorities. The applicants maintained that the reason for this was that the outlet pipe of Balwearie Dam was of insufficient internal diameter for this purpose and therefore the operation of their prior rights was jeopardized. In this case the two dams have a similar capacity and are separated by a mere 2km where each dam has three participants in the utilization of the stored water. Two parts of water right no. 2276 have the earliest priority, after which water right no. 10156 has its turn. Then the remaining part of water right no. 2276 followed by the other two participants is satisfied. The other two participants in water right no. 10156 then follow each with separate priorities. This rather complex situation involves 6 separate water rights and 9 priorities. An agreement was reached at the Administrative Court between the applicants and the respondents. It was agreed that: ● A siphon of 12 inches diameter be constructed and installed together with an outlet pipe of not less than 12 inches diameter in Balwearie Dam. Both devices were to be used to pass water that flows into Balwearie Dam and down to Tawstock Dam to meet the entitlements of holders of water rights no, 2276, 9101 and 10364 together with the primary requirement of 85 liters per second. ● Not less than 425l/s will be released from Balwearie Dam, and the construction and installation of the siphon and the gauging weir immediately upstream of the headwaters of Balwearie Dam shall be carried out by Balwearie farmers so as to be in full operation.

5 SUMMARY The case has described the way in which the operation of priorities of this complex situation worked under the old system and how the issue of satisfying earlier priorities was resolved. In arbitration (a conflict management tool), the Tawstock farmers submitted their argument before the Administrative Court who acted as the judge and a solution was reached whereby both the Tawstock and Balwearie farmers signed an agreement. 6 RECOMMENDATIONS It is recommended that measures be taken to establish actual water use rather than assume values of water rights so that true commitment levels are achieved. It is also recommended that conflict management play a more important role in water resource management so as to empower local water authorities to handle such situations involving disputes over water allocation. It is hoped these recommendations will lay the platform for increased participation, negotiation and dialogue for better basin management.


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7 CONCLUSION The main objective of this study was to establish how existing water rights in a small catchment were operated under the old system based on the 1976 Water Act and to describe the conversion process with the requirements of the permit system. The results from the study show that most storage rights were operated with staff gauges installed in the basin that enabled the stored volume and abstraction to be determined for any reservoir level. The study also showed that senior water rights consumed water impetuously without much consideration for downstream users and therefore new users found it difficult to receive a full entitlement of water allocated. The new system now allows new users the opportunity to be given an abstraction permit for their beneficial use therefore disregarding priority. The study revealed through a questionnaire that there was little cooperation and communication over data between upstream and downstream users that often resulted in disputes over water allocation. Of the seven farmers interviewed, six of them said they were not aware of the water reform. It is important therefore that water authorities and catchment agencies seriously consider the issue of enhancing dialogue and cooperation between different users and assist in the issuing of water permits to improve the management of water at catchment and basin level. The results of the study showed that the Mswenzi is a highly committed catchment with a total use of flow and storage water rights totaling 6900*103m3/a for all the water right holders in the catchment. The Mswenzi generates on average per year, 11070*103m3/a of water, bringing the water commitment of the catchment to 62.3%. The study showed that in the conversion process from the old water rights into new water permits, the permits would have to use the same volumes as previously granted for their water rights and discard the priority date. Therein catchment councils have the obligation of amending or revising the water permit according to beneficial use of the permits and accommodation of new entries among other criteria. Perceptions of the commercial farmers in the catchment have shown that the majority, almost 80%, of the big stakeholders in the catchment are unaware of the principles of the water reform and how their new water permits will be operated. Conflicts over water allocation have emerged under the old system due to misperceptions and lack of adequate data and it is anticipated that the new permit system will mitigate the grounds for conflicts in the future. REFERENCES Ashton, P. 1999. Southern African water conflicts: Are they inevitable or preventable? In: Water for Peace in the Middle East and Southern Africa, Geneva, Green Cross International, 2000. Biswas, A.K. 1993. Management of International Waters: Problems and Perspectives, Water Resources Development, 9. Heun, J. 1998. Water resources planning and analysis, Lecture Note, Dept. of Civil Engineering, University of Zimbabwe, Harare. Huffaker et al. 2000. The Role of Prior Appropriation in Allocating Water Resources into the 21st Century, Water Resource Development, 16.


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Jaspers et al. 1999. An external review of the Mupfure Catchment Integrated Water Management Project, Prepared for the Royal Netherlands Embassy, Harare. Lang, H. 1997. Options for a New Water Rights System. Draft Unpublished Paper, October. Manzungu, E. 1999a. Conflict management in the Umvumvumvu Catchment, In: Water for Agriculture in Zimbabwe: Policy and Management Options for the Smallholder Sector, University of Zimbabwe, Harare. Manzungu, E. 1999b. Strategies of smallholder irrigation management in Zimbabwe, PhD Thesis, Wageningen University, Netherlands. Manzungu, E, Senzanje, A & Van der Zaag, P. 1999. Water for Agriculture in Zimbabwe: Policy and Management Options for the Smallholder Sector. University of Zimbabwe Publications, Harare. Mazvimavi, D. 1998. Water Resources Management in the Water Catchment Board Pilot Areas, Phase I: Data Collection, CASS Technical Paper, NRM Series; CPN 95/98, University of Zimbabwe, Harare. Natsa, T.F. 1999. From priority date to fractional allocation: Towards equitable distribution of surface water resources in Zimbabwe. MSc Thesis, University of Zimbabwe, Harare. Resolve Inc. et al. 2000. Participation, Negotiation and Conflict Management in Large Dams Projects, Final version, Cape Town, Republic of South Africa. Van der Zaag, P & Nyagwambo, L. 1998. Water Allocation Criteria for the Mupfure Catchment, Final Document, December 1998, Harare. Van der Zaag, P. 2001. Water Law Lecture Notes, Department of Civil Engineering, University of Zimbabwe, Harare. Wallensteen, P & Swain, A. 1997. Comprehensive assessment of the freshwater resources of the world. International fresh water resources: Conflict or cooperation, Stockholm, Sweden. Wolf, A.T. 2000. Indigenous Approaches to Water Conflict Negotiations and Implications for International Waters, Published in: International Negotiation: A Journal of Theory and Practice, December 2000. Zimbabwe 1996. Zimbabwe Water Act 1976, (Chapter 20:22), Government Printers, Harare. Zimbabwe 1999. Zimbabwe Water Act 1998, (Chapter 20:24), Government Printers, Harare.

Impacts of water development in arid lands of Southern Africa: socio-economic issues J.P.Msangi University of Namibia, Windhoek, Namibia Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: Aridity characterizes an expansive area of Southern Africa. By manipulating their environment and available resources, the inhabitants of this area have devised mechanisms that enable them eke a living. Although unfavorable climatic and environmental conditions contribute to precarious living conditions for the inhabitants of the arid lands all over the world, those in Southern Africa are particularly vulnerable due to low technology and high dependence on natural resources exploitation. Many water development projects have been undertaken causing varying environmental impacts that have reduced the performance of the economy and undermined sustainability of projects meant to off set the difficult situations prevalent in the arid lands in Southern Africa. Impacts of such undertakings must be identified prior and after project implementation and mitigative measures taken into consideration during the planning stage. The multisectoral nature of water resource projects should be taken into consideration during the planning and implementation phases. Partnerships and indigenous knowledge are vital in ensuring success.

1 INTRODUCTION Southern Africa has an expansive area that is characterized by aridity, a condition of perpetual moisture scarcity. The inhabitants of such areas have devised mechanisms which enable them eke a living through manipulations of the environment and available resources, water being key to all the activities. The activities of these areas are predominantly changing due to adjustments that must be made in response to the prevailing climatic conditions. Although recurrent droughts, climatic variability and uncertainty heavily contribute to precarious living conditions for the inhabitants of the arid lands all over the world, those in Southern Africa are particularly vulnerable due to low technology and high dependence on natural resource exploitation. Due to the prevailing climatic conditions and high sense of uncertainty, many water development projects have been undertaken or are proposed to provide more dependable water

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supplies to meet both animal and human requirements in Southern Africa. In some areas, irrigation water has been provided to overcome inadequate and/or unreliable rainfall while in others domestic water supply schemes have been constructed including dam building and borehole construction. The main justifying reason for such undertakings is always that water in its natural state is seldom in a position to satisfy the requirements which include public water supply for domestic use and/or livestock production; regulated flow for hydro-electric power production; adequate supplies for industrial processing and irrigated agriculture. Water development projects have been recorded to cause adverse impacts to the environment the world over, Southern Africa included. Such impacts are known to reduce the performance of the economy and undermine the sustainability of projects implemented to off set the difficult situations found in the arid lands. Such impacts need to be identified and/or predicted during the project planning stage so that appropriate mitigative measures can be taken into consideration before and after the project is implemented. Environmental impact issues in Southern Africa include high population concentrations (both human and animal) attracted by the putting up of a reliable water source; soil erosion; agricultural and chemical pollution from irrigated fields as well as over exploitation of groundwater aquifers which may lead to collapse and eventual destruction of the aquifer. Others include denying down stream populations and habitats fresh water supply through damming or excessive abstractions to meet upstream water demands. Through environmental impact studies, the multisectoral nature of water resource development can be taken into consideration during the planning and implementation phases of water resource development projects. Strong partnerships and indigenous knowledge considerations are necessary to make sure all aspects of the resource are included in such studies. 2 INTRODUCTION 2.1 Environmental impact An impact is described as a strong impression or effect on something or even somebody so that a lasting impression is observable and/or measurable (Oxford advanced Learners’ Dictionary). An impact or repercussion of something can also be anticipated or expected or predicted before it takes place. On the other hand, an EIA has been described as a formal study that is used in achieving successful development of major projects through incorporation of environmental considerations in project planning and management (Westman, 1985). An EIA has been identified as both a planning and management tool for sustainable utilization of natural resources. It seeks to ensure that development options are environmentally sound and that any environmental consequences are recognized early and taken into account in project planning, design and implementation. EIA has its origins in USA where during the 1970s initial developments focused on impacts to the biophysical environment and subsequently moved on to encompass and integrate social, health, economic, improved public participation, risk and uncertainty. During mid and late 1980s emphasis included cumulative effects, the integration of project level environmental impact assessment with policy, planning, legislation, monitoring and auditing. During recent times, EIA has been described as “a planning and


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assessment process that involves forecasting the environmental consequences of a proposed development process” (Mubvami, 2000). It involves “identifying, predicting, evaluating and mitigating the biophysical, social and other relevant effects of proposed projects and physical activities prior to major decisions and commitments are made” (Mutter, Topfer & Wichterich, 2002). EIA has evolved into a flexible planning tool that allows governments, donor agencies and project developers to evaluate the environmental implications of project proposals during the planning stage. Since mid 1980s, many investors and funding agencies including the World Bank and other multilateral banks require that their borrowers carry out EIA for proposed projects and programmes. During this time, many lending institutions and international environmental agencies like UNEP issued guidelines to assist such assessments and ensure that projects are designed and implemented in an environmentally sound manner. EIA is now widely accepted in both developed and developing countries as an important tool for project planning. The role, fully acknowledged at the 1992 Earth Summit, has led to several countries putting in place legislation that requires that an EIA be conducted before projects are implemented. The purpose of EIA focuses on providing a systematic, holistic and multidisciplinary view of the impacts of a proposed project or undertaking such as the impacts of constructing a dam across a river valley. These impacts include those affecting the natural environment (both living and non-living) and the people who inhabit and use the specified natural environment. In short, EIA examines the environmental and socioeconomic consequences of a proposed undertaking such as a river development project. It emphasizes prevention or minimization of adverse impacts of the project on the environment and the people. It also looks at the effects of the environmental factors on the proposed project as well as the impacts of the people’s activities on the proposed undertaking. Further, an EIA ensures that the ability of the biosphere to absorb effects of proposed activities is not diminished. It is undertaken in order to identify, analyze and assess potential environmental effects of a proposed project and where possible mitigate against negative effects. An EIA exercise can have varied consequences on a proposed undertaking. It can be used to modify and improve the design of a proposal, it can ensure efficient use of resources, it can enhance the social aspects of a proposal and it can be used to identify measures for monitoring and managing impacts and to provide justification for a proposed activity. The effectiveness of the EIA process will have a direct bearing on how many of these results will be achieved. This is more so in highly fragile and vulnerable ecosystems found over much of the arid lands of the world including those in Africa. Since an EIA is conducted before an undertaking, its ultimate goal should be to ensure that current development meets the needs of the present generations without comprising the ability of future generations to meet their own needs. Thus EIA would contribute towards the attainment of sustainable development. 3 PURPOSE OF WATER DEVELOPMENT Most always, the purpose of water development is to provide adequate supplies of water to meet various water demands. This is necessitated by the fact that in most instances,


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water in its natural state is not in a position to satisfy the numerous demands placed upon it, which may include: – Public water supply for domestic use; – Hydro-electric power production; – Irrigated agriculture development; – Water for livestock production; – Industrial water for processing or for cooling machines; – Water for sewage treatment; – Fishing; – Navigation; – Recreation. Water development projects are known to cause both positive and adverse environmental impacts to the environment that need to be identified and/or predicted prior to project implementation. Examples range widely depending on the nature and scale of the project, its location and the type and level of technology required for its sustainability. A good example is where a project involving groundwater recharge using wastewater must take into consideration the danger of pollution from the wastewater from industrial and residential sources. The cost of treatment of the water before using it to recharge ground water must be considered included in the assessment. Similarly, the impacts of other land use management activities taking place in the project area are known to affect the water projects. Activities of unprotected catchment areas including unplanned deforestation and/or overgrazing would produce sediments which would reduce the capacity and adversely affect the life span and operation of a down stream reservoir greatly undermining the project performance and disrupting its sustainability such as happened in Kisongo dam in Arusha and Imagi dam in Dodoma, Tanzania (Msangi, 1987; Kitheka, 1993; Christiansson, 1981). On the other hand a well-managed cultivation system (including terracing and aforestation) of a catchment area will prolong the life span of the reservoir making it possible to meet multiple demands from its waters. All the occurring impacts need to be identified and/or predicted during the project planning stage so that appropriate mitigative measures can be considered before a project is implemented. Needed also is post planning project monitoring to assess the impacts resulting from the undertaking. 4 ASSESSMENT OF ENVIRONMENTAL IMPACT OF WATER DEVELOPMENT PROJECTS In the process of considering whether to carry out a major water project or not, the first main concern is the extent of environmental change that will result from the construction and particularly after the project is implemented. This change will be both to the physical environment as well as to the people and other living organisms inhabiting that environment. The changes to the physical environment will influence the socialeconomic environment just like the people’s response to the physical change will affect the physical environment. Thus both types of change must be considered when impacts are predicted and later on monitored. Most of the changes will be permanent and in some


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cases cumulative. Alternatives form part of the pre-implementation phase when impacts are weighed and compared to provide careful and sufficient consideration of all possible impacts, both negative and positive ones. The assessment process for water development projects mainly addresses environmental impacts resulting from the project itself and land use management practices occurring in the river catchment area. These impacts could include high surface runoff; soil erosion and increased sediment flow and raised concentrations that are a result of induced land use changes in a river catchment where a project is proposed. Moreover, lack of knowledge or lack of apprehension of the consequences of overgrazing the catchment areas contributes to the shortening of the life span of a project (Msangi, 1996). Changed ecological conditions, such as the creation of an ideal habitat for disease carrying flies, snails and mosquitoes, have also made areas around a reservoir created behind a dam undesirable and unhealthy (Kaduma, 1977; 1972). Other impacts may include changes to groundwater levels, changes to river flow and flow peaks, flooding or drying up of a river (Christelis & Struckmeier, 2001). Others could be introduction of agricultural chemicals and fertilizer residues by surface runoff from farmlands where irrigated agriculture is part of the project or where the project will induce such undertakings. An indirect impact on an undertaking emanates from the attitudes of the population towards the proposed project as well as attitudes held on water resource use and management. In some parts of the dry lands in Southern Africa, attitudes centering on cattle numbers as wealth are most likely to override environmental conservation so that once water becomes available, the number and intensity of grazing increases without due regard to carrying capacity of the range (Msangi, 1992; 1996; Darkoh, 1989; Ellis & Swift, 1998). Such attitudes and other related social practices should form part of the assessment during and after implementation of a water development project. The actual impacts of a water resource project depend on the purpose, scale and location of the project. For a small water supply project for example, the positive impacts will include the expected socio-economic benefits such as drinking water and water for other domestic uses. Raised health and sanitation standards and the general well being of the people will also be included. An indirect impact will include elevated economic standards, as people enjoying good health will be able to work to produce more and thus generate some economic returns. On the other hand negative impacts will include over grazing of the land around watering points and beyond, along animal tracks and adjacent land etc (Darkoh, 1989; Msangi, 1991, 1996; Stone, 1991). For a large water supply project with pipelines and house connections and staggered animal watering points, the adverse impacts on the physical environment would be minimized or controlled completely. Thus alternatives ought to be considered carefully before implementation. A water development project involving the construction of large structures such as dams and canals will produce a varying range of impacts on both the physical and socioeconomic environments. Possible adverse impacts could include the displacement of people and animal populations as happened when Lake Kariba and other large dams in Southern Africa (Kaduma, 1997) and others including loss of flora and fauna; changes in groundwater conditions, triggering seismic activity due to the presence of a large body of water; deterioration of the health status of the environment through creation of ideal habitats for disease vectors; lowered water quality from rotting inundated vegetation and altered river flow characteristics (Kaduma, 1997). Conversely, the advantages of a large


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scale water development would include creation of new habitats such as wetlands; the production of much needed electricity for irrigation water to support agricultural production; provision of hydro electric power for homes and for industrial establishments; job creation from undertakings utilizing the water and generated power; support improved economic conditions and the well being of the people; regulated river flow and improved utilization of a river including the establishment of a fishery. The list of indirect impacts is long and varied. The creation of sub-surface dams that are more environmentally feasible than surface dams are faced with various limitations including water recovery. High investments required during construction and maintenance and operation of pumps (be it petrol/diesel, solar energy or windmills) are often not economically justified given the low land productivity inherent in most parts of the dry lands of Southern Africa. Hand pumps are only feasible if recovery is from shallow wells (Msangi, 1996). 5 DRY LANDS IN SOUTHERN AFRICA Southern Africa has an expansive area that is characterized by aridity, aridity being a condition of perpetual moisture scarcity. The inhabitants of such areas have devised mechanisms which enable them eke a living through manipulations of the environment and available resources. The activities of these areas are predominantly changing due to adjustments that must be made in response to the prevailing climatic conditions. An exceptionally wet year may see the cultivation and harvesting of quick maturing crops that dry years will not. More often than not the survival techniques include livestock rearing, mostly keeping of small stock such as goats and sheep. Cattle are kept for milk, export beef and as a source of wealth in the areas that enjoy relatively humid conditions as opposed to those that are very dry (Msangi, 1996). Due to excessively high temperatures, the little moisture that may be received in the form of rain gets evaporated very quickly soon after a downpour (Msangi, 1996). Climatic variability and uncertainty has led to precarious living conditions for the inhabitants of the arid lands all over the world, those in Southern Africa high in the list. Due to the prevailing climatic conditions and high sense of uncertainty, many water development projects have been undertaken or are proposed to provide more dependable water supplies for both animal and human requirements as well as industrial water needs. In others, irrigation water has been provided to overcome inadequate and/or unreliable rainfall (Chenje & Johnson, 1996). The main justifying reason for such undertakings is always that water in its natural state is seldom in a position to satisfy the requirements which include public water supply for domestic use; regulated flow for hydro-electric power production; adequate supplies for irrigated agriculture development and for livestock production. Water development projects have been recorded to cause negative impacts to the receiving environment (Kaduma, 1977). While these have been investigated and documented worldwide, in Southern Africa, the need still exists to identify and/or predict them before the proposed projects are implemented and follow up monitoring after they are in operation (Chenje & Johnson, 1996; Wood, Stedman & Mang, 2000). Such projects need to be monitored as they may be affected by environmental factors caused by other land use management activities taking place in the


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project areas. Such activities are known to reduce the performance of projects and do undermine the sustainability of projects implemented to off set the difficult situations found in the arid lands (Biswas, 1978; Msangi, 1996). All these impacts need to be identified and/or predicted during the project planning stage so that appropriate mitigative measures can be considered before the project is implemented. The inhabitants of the dry lands in Southern Africa have a rich heritage of managing and living with their environment including water. They have been irrigating their lands for centuries. The communities inhabiting the dry lands have lived and adapted to the environmental conditions arising from many years of experience and folklore handed down generations. This harmonious existence with nature was interrupted and interfered with during the last a hundred years or so through the introduction of western cultures and new ways of viewing the environment. The introduction of improved health and nutritional facilities as well as monetary economy together with the institutional requirements that go with it, has disrupted and partially changed the lifestyles of these communities (Msangi, 1996, 1992; Stone, 1991; Ellis & Swift, 1988). The population of both people and animals has increased rapidly as food aid and western medicine have increased survival chances and increased fertility rates. Before this interruption, land, water and vegetation successfully supported the life styles and economic activities of the dry lands inhabitants. The forces of nature had adequately checked imbalances between man and nature so that simple social and economic patterns had developed and had been harmoniously maintained. The installation of schools, hospitals, central governments and all their branches imposed new requirements on the communities and therefore the environmental resources. Water being the central and most scarce resource in these lands has been subjected to various manipulations and new development approaches geared towards meeting both the communities’ traditional and new institutional demands. Due to increasing populations of both people and animals, water demand far exceeds supply, thus the need to practice wise use, management and conservation of water resources in the dry lands of Southern Africa. This requires that social attitudes be reoriented so that communities appreciate the implications of limited supply as opposed to the ever increasing demands on the scarce water resources, limited groundwater recharge rates and the need to conserve the resources such as controlling pollution and recycling, all new concepts to most of the dry land communities in Southern Africa. Many cases of efforts to conserve, develop and manage the water resources in the dry lands have been made and are documented in numerous plans and consultant reports (Msangi, 1992). Few successful cases have been recorded and many failures have been experienced. The reasons for failure are mainly due to the inappropriateness of the technology adopted to the existing environmental conditions or, most often, to the wants and wishes of the local communities. Many times the wrong sector of the community has been targeted for training. Women and their children who are the ones mainly responsible for collecting and managing water for domestic use and sometimes tending small stock, tend to be side lined for the men who are users rather than managers of the resource. Women should be at the center of any training aimed at improving existing management technologies or introducing new ones. Sustainability rests on clear understanding of the people’s social organizations and gender roles and economic patterns in a given community.


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Economic and other development activities intended to be introduced into the dry lands should be focused more on the needs and wants of the people bearing in mind environmental constraints. For example instead of introducing irrigated agriculture, dry land farming based on indigenous crop varieties should be employed instead of sprinkler irrigation to grow exotic crops with high water demand. Flood irrigation and other high water requiring methods of crop growing have rendered useless large tracts of land through salinization. The high evaporation rates inherent in the dry lands of Southern Africa do not favor these methods. 6 LAND USE MANAGEMENT SYSTEMS AND THEIR IMPACTS ON WATER DEVELOPMENT PROJECTS Water development projects are affected by the land use in many different ways. Unregulated land use system such as indiscriminate clearing of tree cover from a catchment area can lead to reduced water yield and cut short the lifespan of a project. Cultivation and/or heavy grazing of such a catchment area can lead to soil erosion and subsequent sedimentation and siltation of a reservoir, intakes and irrigation channels. Such a system can also lead to increased surface runoff, flooding in the lower reaches and lowered groundwater in the upper reaches thus jeopardizing a water development project. Other impacts include reduced water quality from suspended sediment and agricultural chemicals and residues from farmlands. This will lead to increased costs for water purification or adverse health conditions for those depending on the water source either for domestic use or industrial processing. Habitats for fish and other aquatic animals will be damaged and the economic standing of those dependent on them will be adversely affected. Furthermore, maintenance costs for structures will increase dramatically if sediment has to be cleared regularly, unless ofcourse this was foreseen and budgeted for right from the beginning. Closely connected to decreased infiltration and reduced water yield due to compaction is the loss of water sources such as wells and springs. Reduced infiltration leads to reduction in levels of ground water table that may cause ground subsidence (ground surface collapse and curving in) due to over pumping; or if close to coastal areas lead to intrusion of coastal salt water and soil salinization that may reduce crop production through increased accumulation of harmful salts in soil particularly where irrigated agriculture depend on wells or boreholes (Christelis & Struckmeier, 2001). Other types of land use such as urban land use may cause water pollution due to inadequate water and waste management from dwellings and industries. Pathogens as well as organic and chemical pollution can lower the water quality necessitating expensive water treatment to meet set water quality standards. Alternatively, high concentrations of discharged organic compounds may create excessive demand on oxygen resources of a body of water during the conversion process to the extent that the oxygen concentration in the water is reduced and eventually depleted resulting in death of living organisms including fish. High concentration of organic matter may also raise the fertility of the water body to the extent that eutrophication occurs leading to life decimation in the water body (Wood, Stedman & Mang, 2000).


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7 CONCLUSIONS AND RECOMMENDATIONS It becomes apparent that water resource development projects produce serious and definable impacts on a community both socially and economically while other activities in the vicinity of the water projects affect and influence the performance of the projects. Feasibility studies for all impacts must be carried out prior to water projects implementation. Successful water development and resource conservation should always strive to incorporate environmental considerations during project planning and project implementation stages. Similarly, integrated catchment management should encompass the various resource components and associated management practices to achieve stable systems. Environmental legislation should make EIA mandatory in all water development projects in order to ensure sustainability and high quality water supply for industrial, agricultural and domestic usage. People centered planning should be adopted where social, economic and environmental consequences of an undertaking are given deserving emphasis. Therefore social-economic as well as environmental impacts should be considered alongside the often-emphasized physical and technical impacts. 8 APPENDIX 1 (AFTER WESTMAN, W.E. 1985) Questions Useful in Planning the Pre-Impact Phases of an Impact Assessment: 8.1 Phase I: Defining study goals What information is needed and how precise must it be for: – The proponent to minimize environmental impact. – The government agency to reach a decision on approving the project. – Concerned groups to know how they will be affected What resources are needed for the study? What resources are available? – Needed expertise; available expertise – Needed time for baseline and experimental studies – Remaining time before the project is supposed to begin – Required funds to conduct the proposed study; available funds. 8.2 Phase II: Identifying potential impact What are the boundaries of potential impacts? – Area affected – Organisms or ecological functions affected – Duration of the project


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– Interval before effects occur – Duration of effects with and without mitigation. What is the range of potential impacts? – Major direct actions – Major ecological components (air, land, biota, structure) affected – Major ecological processes affected – Secondary or higher-order interactions – Indirect effects triggered at a future time or different place – Other actions (past, present, reasonably foreseeable future) that may add to the present action, causing cumulative effects. Which potential impacts are most significant? Which effects will: – Violate existing laws, plans or policies. – Cause major disruption to ecosystem processes, processes, affecting species significantly. – Cause major adverse effects on species numbers. – Cause health risks, economic losses or significant social disruption to people. 8.3 Phase III: Measuring baseline conditions and predicting significant impacts Baseline conditions: What are the significant features of the ecosystem presently? – What is the current pattern of fluctuation in popular sizes for important species (measured over sufficient time to characterize the range of variations)? – Which species are playing a dominant or critical role in maintaining ecosystem processes? What is their abundance, distribution and function of behaviour? – What is the condition (Quality, quantity, dynamics) of physical resources of the ecosystem? – What are the major pathways of interaction between ecological components? – What sources of stress from natural or human-induced sources already exist (fire, air pollution, grazing etc)? With what intensity and periodicity do these stresses occur? Predictions: What will be the major effects of the proposed action? What is known from each of the following? – Case studies: Extrapolation of effects from similar instances of disruption to the same or similar ecosystems elsewhere. – Modelling: Predictions from conceptual or quantitative models of ecosystem interaction. – Bioassay and Microcosm Studies: The effects of simulated disturbances on ecosystem components under controlled conditions. – Field Perturbation Studies: Response of a portion of the proposed project area to experimental disturbance.


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– Theoretical Considerations: Predictions of effect from the current ecological theory. Estimation of likelihood: – What is the probability of occurrence of the predicted events? – How precisely can the magnitude and likelihood of impacts be estimated? Summarizing and analyzing findings: – How can findings be summarized in table, graphs or indexes so that key findings emerge? – What is the ecological interpretation of the findings? 8.4 Phase IV: Evaluating significance of findings How are the effects distributed among the affected groups? – What is the nature and magnitude of impact on each affected group? – What weight shall be given to the concerns of each group? – What weight does each group give to the significance of predicted effects? How well are goals achieved by the proposal? – Proponent’s goals? – Goals of affected groups? What is the overall social significance of the predicted ecological effects? – How can effects be expressed in terms that allow meaningful comparison with other social goods, services and values? – If monetary values are placed on normally unpriced goods and services, what features are inadequately evaluated by this procedure? 8.5 Phase V: Considering alternatives to the proposed action – What would be the effect of not proceeding with the project? – What would be the effect of achieving ultimate project goals by an entirely different means? (e.g. maintaining electrical service to a growing population by conserving energy rather than building a new power plant) – What alternative designs could achieve project goals? What steps could be taken to mitigate adverse environmental effects of the proposed project? – Could parts of the proposal be reduced or eliminated? – Could expected damage be repaired or rehabilitated? – Could ongoing management procedures be instituted to reduce damage?


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– Could affected components be replaced or owners compensated? – Could project design be modified to reduce effects? – Could effects be monitored, and provision made for future mitigation of project effects when the exact nature and extent of effects are better known?

REFERENCES Chenje, M. & Johnson P. (eds.) 1996. Water in Southern Africa. SADC, IUCN SARDC, 238 Biswas, A.K. 1978. Environmental Implications of Water Development for Developing Countries, Water Supply and Management Journal, 2, 283–297 Christelis, G. & Struckmeier, W. (eds) 2001. Groundwater in Namibia: An explanation to the Hydrological Map, 128 Christiansson, C. 1981. Soil Erosion and Sedimentation in Semi-arid Tanzania: Studies on Environmental Change and Ecological Imbalance. Uppsala: Scandinavian Institute of African Studies and Department of Physical Geography, University of Stockholm. Darkoh, M.B.K. 1989. Combating Desertification in the Southern African Region: An Updated Regional Assessment. Nairobi: UNEP Ellis J.E. & Swift, D.M. 1988. Stability of African Pastoral Ecosystems: Alternative Paradigms and Implications for Development. Journal of Range Management, 41(6), 450–211. Kaduma, J.D. 1972. Some Development and Economic Aspects of the Mindu Dam Project, Morogoro: A Background Analysis for Decision Making, M.A thesis, University of Dar es Salaam, 140 Kaduma, J.D. 1977. Man-made Lakes: Their Social, Economic and Ecological Impacts—The Case in Tanzania, PhD thesis, University of Dar es Salaam, 400 Kitheka, J.U. 1993. Soil Erosion and Its Impacts on Surface Water Reservoirs: A Case study of Nguu Tatu Catchment, NE Mombasa District, Kenya, Proc. 4th Land and Water Management Workshop, Nairobi, Kenya, 309–329 Mubvami, T. 2000. Environmental Impact Assessment as a Policy Tool for Environmental Management. IUCN-ROSA A Handbook on Approaches to the Environmental Policy Analysis in Southern Africa. IUCN—The World Conservation Union. Mutter, T., Topfer, J. & Wichterich, C. 2002. A Comprehensive Study of the Heinrich Boell Foundation’s projects abroad in Political Ecology and Sustainability. 1st Ed. Heinrich Boell Foundation. Msangi, J.P. 1987. Conservation of Water Resources in the Semi-arid Areas of Tanzania. Journal of Eastern Africa Research and Development. Vol 17, 63–73. Msangi, J.P. 1991. Sustainability in Exploitation, Development and Management of Hydrological Resources of Turkana District. Journal of Eastern African Research and Development, 21, 21– 39. Msangi, J.P. 1992. Social-Cultural and Demographic Factors in Desertification Control in Kenya’s Arid and Semi-arid Lands. Proc. of the Workshop on Desertification Monitoring, Assessment and Control. Nairobi: National Environment Secretariat, 21–32. Msangi, J.P. 1996. Social-Cultural Factors Affecting Non-Adoption of New Water Harvesting Technology Among the Dryland Communities in East Africa. In Yue-man Yeung (ed) 1996 Global Change and the Commonwealth. Hong Kong Institute of Asia-Pacific Studies, Chinese University, Hong Kong, 233–253. Stone, J.C. (ed) 1991. Pastoral Economies in Africa and Longterm Responses to Drought. Aberdeen: Aberdeen University African Studies Group. Wood, A. Stedman-Edwards P. & Mang, J. 2000. The Root Causes of Biodiversity Loss. Earthscan, 399.


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Westman, W.E. 1985. Ecology, Impact Assessment, and Environmental Planning. John Wiley & Sons.

Institutional challenges for small towns’ water supply delivery in Ghana Kwabena Biritwum Nyarko Kwame Nkrumah University of Science and Technology, Kumasi, Ghana Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: The small towns’ water supply sector emerged in Ghana after 1994 when water supply delivery was separated into urban water supply (served by a public utility) and Community Water Supply (CWS) decentralised under community ownership and management. A small towns’ water system, which falls under CWS, is defined as a piped system serving a community with inhabitants between 2,000 and 50,000 that is willing to own and manage its water supply system. A national programme for community water delivery has been in place since 1994. Ensuring the sustainability of the small towns’ systems are fundamental concerns, which makes the study of institutional issues that affect the sector timely. The paper describes how the institutional arrangement to support the delivery of small towns’ water services in Ghana has evolved, and also discusses the experiences, lessons and the challenges. The paper also makes recommendations to improve service delivery.

1 INTRODUCTION About 32% of the Ghanaian population do not have access to safe water (WDI, 2002) making access to safe drinking water a challenge. The situation is even worse in the rural an small communities where the majority of the population lives. In 1994, water supply delivery in Ghana has been separated into urban water supply (served by a public utility, GWCL) and Community Water Supply (CWS) under community ownership and management (Nyarko, 2000 & CWSA, 2003a) to improve the supply of water to the people of Ghana in a sustainable manner. Community water supply consists of rural and small towns’ water supply. The small towns’ water supply is a piped system, serving communities with inhabitants between 2,000 and 50,000 who are willing to own and manage the water system. As at the end of 2001 there were 254 small towns’ water supply systems under community ownership and management (CWSA, 2003a). These systems are decentralised and do not enjoy any cross subsidies and other benefits of economies of scale as the urban water supply.


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Consequently, interest in the delivery of water services in small towns has grown rapidly in recent years due to the peculiar characteristics of the small towns and the number of inhabitants it serves. To ensure the sustainability of the small towns’ systems are fundamental concerns, which makes the study of institutional issues that affect the sector timely. This paper examines the institutional framework of the small towns’ water supply component of community water supply with the aim of enhancing the sustainability of the service delivery.

2 BACKGROUND TO THE SMALL TOWNS’ WATER SECTOR 2.1 Historical development of community water supply sub-sector The Ghana Water and Sewerage Corporation (GWSC), the predecessor of Ghana Water Company Limited (GWCL), was established in 1965 by Act 310 for the provision, distribution and conservation of both the urban and rural water supply in Ghana, for public, domestic and industrial purposes. In 1986, the first attempt to enhance service delivery in the rural areas (defined as communities with less than 5000 inhabitants) led to the establishment of the rural water department within the GWSC (Asamoah, 1998). At that time, the approach of providing water services to customers was a supply driven one. With more promising revenue from the urban areas (with higher income levels) as well as technically challenging “engineering” of providing urban water services, GWSC focused more on the urban areas. In 1991, the sector ministry for water, Ministry of Works and Housing (MWH) organised a workshop to discuss the provision and sustainability of rural water supply and sanitation. The outcome of the workshop was the National Community Water and Sanitation Programme (NCWSP), which aims at accomplishing the following objectives: ● To provide basic water and sanitation services to communities that will contribute towards the capital cost and pay the normal operations, maintenance and repair cost of their facilities ● To ensure sustainability of these facilities through community ownership and management, community decision making in their design, active involvement of women at all stages in the project, private sector provision of goods and services, and public sector promotion and support ● To maximise health benefits by integrating water sanitation and hygiene education In line with the NCWSP, the urban and rural water supply systems were separated in 1994. The rural water division of GWSC was transformed into a semi-autonomous department known as the Community Water and Sanitation Department (CWSD), with the responsibility of implementing the NCWSP. CWSD was further transformed by Act 564 of 1998 into an agency, the Community Water and Sanitation Agency (CWSA) (GOG, 1998) with the responsibility of facilitating community water and sanitation services under community ownership and management.

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2.2 NCWSP and GOG decentralisation reforms The implementation strategy of the National Community Water and Sanitation Programme (NCWSP) is consistent with the Ghana decentralisation policy, which transfers authority, responsibility and capacity from the Central Government, Ministries and Departments to the District Assemblies. The decentralisation policy is backed by the Local Government Act, 1993, Act 462, which aims at devolving central administrative authority and divesting implementation responsibility to district levels (GOG, 1993). It re-assigns functions making Central Government Ministries/Departments undertake policy planning, monitoring, evaluation and promotion; and makes regions, (through the Regional Co-ordinating Councils and their respective Regional Planning Co-ordinating Units), play the role of co-ordination, whilst, the District Assemblies become responsible for implementing development programmes (CWSA, 2000). 2.3 The small towns water supply sub-sector A small town is defined in the CWSA Act as “a community that is not rural but is a small urban community that has decided to manage its own water and sanitation systems”(GOG, 1998). A small town water system is also defined as a piped system serving communities of between 2,000 and 50,000 inhabitants who are prepared to manage their water supply systems in an efficient and sustainable manner (CWSA, 2003b). The Act further defines a rural community to be those with less than 5000 inhabitants. The MWH’s Comprehensive Development Framework 1999 for the water sector also defined a small town based on a population range of between 5–15,000 (MWH, 1999). The implementation of each Small Towns’ Project follows the following cycle (CWSA 2003b): ● Project Promotion—for the prospective Community to be familiar with the project cycle and procurement procedures. ● Community Selection and Approval—by the District Assembly in collaboration with the CWSA. ● Community Mobilisation—An extension team is engaged to provide relevant community mobilisation and extension services in each beneficiary community. ● Hygiene Education and Sanitation ● Participatory Planning—to ensure that beneficiary communities are adequately informed and are responsible for decisions made on the system ● Design-Water supply systems shall be adequately designed to provide reliable and good quality water in sufficient quantity over the design period. ● Construction, Operation and Maintenance of the facility ● Post Project—The CWSA shall provide relevant post project support (up to one year) to beneficiary communities to promote achievement of system sustainability. A typical small towns’ water system consists of the following (Jonah. E, 2003): ● a source (usually a mechanised borehole),


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● pump house (a submersible pump powered by a 3-phase voltage transformer), ● source of power (AC power from the national grid, local diesel Power generator or Solar panels (only few cases in the northern region) ● Pipelines (transmission and distribution pipes made of uPVC and HDPE), ● An elevated reservoir, standpipes and appurtenances.

3 POLICY, LEGAL AND INSTITUTIONAL FRAMEWORK 3.1 Institutional arrangements The institutional framework is shown in Fig 1. CWSA is under the oversight of the Ministry of Works and Housing (MWH), the sector ministry responsible for water. The District Assemblies (DA) is the highest political and administrative authority in the district, with responsibility for development and management of basic infrastructure, municipal works and services (GOG,

Figure 1. Institutional arrangement for small towns’ water supply delivery. 1993). The Regional Co-ordinating Councils (RCC) and their respective Regional Planning Co-ordinating Units, play the role of co-ordination, whilst the District Assemblies are responsible for implementing development programmes.


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The Environmental Protection Agency (EPA), under the Ministry of Environment Science and Technology (MEST) is charged with environmental regulation. The Water Resources Commission (WRC) has the obligation to allocate and grant water rights. The Ministry of Finance (MF) is responsible for negotiation and approval of credit facilities (loans) in the water supply and sanitation industry. The CWSA regional officers constitute the Regional Water and Sanitation Team (RWST), which is composed of a Hydrogeologist, Water and Sanitation Engineer, an Extension Services person and a Financial Specialist. The District Water and Sanitation Team (DWST) is the focal point in the District Assembly (DA) for water service delivery. It’s a three-member team with members seconded from the Public Works Department, the Department of Community Development and the Department of Environmental Health. Their role includes the identification of interested communities and providing support to the Water and Sanitation Development Board (WSDB). The External Support Agencies (ESAs) provide technical and funding support to the subsector. The WSDB is responsible for the management of the small towns’ water supply system. It is composed of elected community (small towns) members. The WSDB is also responsible for appointing the operational staff, promoting and disseminating information within the community, ensuring that all community members participate in decision making, setting tariff and ensuring proper financial management. 3.2 Policy framework Based on the January 2001 draft policy for small towns’ water supply (CWSA, 2001) the key policy statements were: ● Beneficiary communities would pay a part of the capital cost and take up all operations and maintenance costs. The community contribution depends on the levels of service selected by the community. It is 5% of the capital cost for Basic Water Supply Services, which is the supply of 20l/c/d (standpipes) for 80% of population and 60l/c/d (house connection) for 20% population. For higher levels of service the community contribution shall be 50% of the capital cost. ● District Assembly shall contribute 5% of the capital cost. ● Water produced shall meet WHO International Drinking Water Quality guidelines. ● Delivery of water should be in a cost effective manner (not exceeding the cedi equivalent of $1.0/m3) CWSA has reviewed the 2001 draft policy in attempt to improve service delivery. The main changes and additions based on the 2003 draft policy for small towns’ water supply (CWSA, 2003b) are: ● Community contribution for capital expenditure would be 2.5% for Basic Water Supply Services and 50% of the Additional Cost for Levels of Service Higher than Basic Water Supply Services; ● The membership of WSDBs shall exclude Traditional Authorities and DAs. Where necessary, they may participate in WSDB meetings as observers. ● Tariffs shall be set by the WSDBs in accordance with CWSA approved tariff setting guidelines. DAs shall review and approve all tariffs. Any reduction in expected tariff


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revenue as a result of action by the DA, e.g., reduced tariff, etc., shall require that the DA pay the difference in revenue into the WSDB account. The CWSA in collaboration with the Regional Co-ordinating Council (RCC) shall ensure compliance. ● The implementation of small towns’ water supply and sanitation projects shall be in accordance with the regulations of the Environmental Protection Agency (EPA) and Water Resource Commission (WRC). The CWSA Guidelines for operations and maintenance (CWSA, 2003c) also stipulates that: ● communities through tariffs shall undertake all major repairs and replacements. But for total rehabilitation, cost sharing arrangement and procurement procedures shall be the same as for new systems. ● Water produced shall meet Ghana Standards Board Drinking Water Quality standards. 3.3 Legal authority of the WSDB The concept of community management is achieved by having community representatives, the Water and Sanitation Development Board (WSDB) in charge of the water supply management in the community. As part of the decentralization policy of the Government and in accordance with section 15 of Act 462 the District Assembly has the power to delegate its functions other than its legislative functions to an individual or group (GOG, 1993). The Water and Sanitation Development Board (WSDB) takes its legal authority from the District Assembly through a byelaw. CWSA has developed generic bye-laws for WSDBs to adapt for their local circumstances.

4 INSTITUTIONAL ANALYSIS OF THE SMALL TOWNS’ SUBSECTOR The research approach utilised both quantitative and qualitative methods to gain insight into the institutional issues of the sector. A literature review of small towns’ water sector project documents was first conducted to get a thorough understanding of the sector. Literature on institutional issues such as what the institutional framework should offer was also reviewed. Based on the literature review, the research instruments (interview guides and questionnaires) were developed for the various stakeholders, in the sector to identify the main institutional issues and challenges. Specific institutional analysis tools used were a combination of the Activity Responsibility Matrix (ARM) and the Strength Weakness Opportunity Treats (SWOT) as well as National Macro-environment Analysis. The data was collected from field visits conducted in 20 small towns’ water supply systems, five district assemblies and three regional CWSA offices. In addition discussions with 20 WSDB Chairmen and 22 Technical Managers who attended a short course at Kwame Nkrumah University of Science and Technology, Kumasi, Ghana in August 2003 were used to validate the study.


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4.1 SWOT Analysis of the STWSS sub-sector See Table 1. 4.2 Activity responsibility matrix See Figure 2.

5 DISCUSSION OF KEY ISSUES 5.1 Institutional arrangement and framework The District Assemblies (DAs) are the managers of the NCWSP at the district level. The DAs full time field team for water and sanitation is the DWST. As mentioned already the DWSTs have been seconded from different departments and are ultimately answerable to their respective regional directors, who can effect transferred without consulting the district assemblies. There are cases of such transfers to different district on a totally different assignment. It was revealed that the time taken for the vacancy to be filled normally spans 3–12 months, after which re-training would have to be organised. It was also realised that the monitoring and supervision of the WSDB activities by the DAs is weak. For example, there are no proper monitoring mechanisms to ensue that records (operational,

Table 1. SWOT analysis. Strengths • •

•

•

•

Weakness

• The DWST is not well anchored in High sense of ownership among the DA structure since the communities Almost universal acceptance of the need individual members have been seconded to the DA making DWST to pay for water services even at rates staff subjected to indiscriminate higher than what prevails in the urban transfers by their mother water sector organisations. Users’ perception of the water service delivery is high, since in most cases the • The technical/administrative water situation was poor before the capacity at the local level (DAs, boards took over. WSDB) is weak. • Data collection and record-keeping In a number of situations, the responsiveness of WSDBs/Communities have been poor, regular water quality monitoring has not yet in servicing breakdowns is high, started; compared to the previous situation of centrally-managed systems under • Even though the various boards GWCL. have been taught the guidelines for Accountability to the users in the tariff-setting, in a majority of the community via public fora. systems visited, the tariff was not based on a rational analysis of the cost components


Opportunities • Government of Ghana support

•

Good will and support from External Support Agencies

•

Government decentralisation policies

282

• Regulation and monitoring from DAs is poor and in most cases no reports are sent by the WSDBs. Even where these are sent no analysis or follow-up is done by the DAs; • Lack of appropriate institutions at the local level to manage the water resource • Revenues accruing from water sales are sometimes mis-appropriated for other purposes; • Membership of some boards is dwindling due to a lack of interest, presumably because of the poor remuneration. This leaves a few who take decisions that may not always be in the interest of the whole. Threats • Political interferences in community management (WSDB affairs). • Relatively high levels of tariff in small towns’ compared with the urban water supply • ESAs/Donor fatigue • Inadequate attention to ensure water resource management • Inadequate attention to ensure financial sustainability

technical and financial) are well kept and that reports are submitted to DAs and CWSA. In addition, when reports are prepared and sent to the DAs it hardly get comments from the DAs. Majority of small towns does not perform routine water quality tests as stipulated by CWSA. This has been attributed to low capacity at the DA level especially the DWST to perform their function and inadequate resources at the DWSTs disposal for their duties. The DAs is also expected to play the role of the Water Resources Commission (WRC) at the district level in the areas of water abstraction rights and permitting. This aspect is not yet operational at the DAs level. The Ministry of Works and Housing (MWH) is responsible for policy making in the water sector. The provision of infrastructure is the responsibility of the DAs, which is under the Ministry of Local Government and Rural Development (MLGRD). CWSA as a facilitating agency cannot force the DAs or the community (WSDB) to execute its water related activities (eg. ensuring the submission of periodic reports, water quality monitoring and using appropriate water tariffs). This is attributed to the following: lack of effective accountability mechanisms between MLGRD/DA and CWSA; the location of


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CWSA and DAs in different ministries and the fact that the DAs is an authority on its own.

Figure 2. Scored activity responsibility matrix. To improve on the situation the following option are considered important. First, establish a works department under the DAs structure with responsibility for infrastructure (including) delivery so as to deal with CWSA. This has been accepted in principle but its implementation is yet to start. Secondly, establish clear and explicit accountability mechanism with benchmarks between the RWST and the DAs within the region would help. The introduction of yard stick competition with incentives for the DAs in a particular region or even nationwide would be useful to provide a check on the DAs to enhance performance. It is important for the CWSA regional team to have good collaboration with the RCC the appropriate institution to supervise the DAs activities to enhance CWSA monitoring role of the NCWSP. The roles and responsibilities of the WSDB demand certain skills, such as technical, financial, managerial etc. The selection criteria initially specified gender and interest groups representation, without mention of the skills required. The new draft policy dated July 2003 adds that the membership of WSDBs shall exclude Traditional Authorities and DAs, but where necessary, they may participate in WSDB meetings as observers (CWSA, 2003b). This is laudable since there were interference from traditional authorities. For example in one small town the WSDB chairman was the chief and his nephew was also the treasurer. In a number of communities political agitation and social tensions have affected the membership, tenure and therefore the effectiveness of WSDBs. Some of the examples are:


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● In a small town (Bimbilla), after a meeting with all stakeholders to increase the tariffs “a youth movement” managed to convince the District Chief executive (DCE) to reverse the decision. ● In a small town (Bekwai), the District Security Council dissolved the WSDB in response to a proposed demonstration threat by some community members. However, the WSDB were re-instated after about six months. ● In a small town (Juaso) the chief requested for money for farming and was granted by the WSDB. The DA got to know of it and demanded the money back and the WSDB was dissolved. As at now (over 6 months) the new WSDB do not have access to their Bank accounts because signatories have not changed. At a recent training course organised at KNUST for WSDB treasures, majority of the participants confirmed having illiterates on the WSDB and indicated that it affects performance. They attribute that to the community sensitisation during project preparation, which made them understand that the WSDB is the community representative and that any one elected by the community could do it. As a result some of the WSDBs members do not understand the issues, and this reflects in the system’s performance. In cases where members have the required skills, performance has been exceptional (Arthur, 2002). The field visits also revealed that, WSDB perceives themselves as owners of the water supply, which seems to explain why periodic operational reports are not sent regularly to the DAs and CWSA. The DAs also do not have incentive mechanisms in place to enhance the WSDB performance. Most or some of the WSDB do not have approved byelaws and hence do not have legal recognition. 5.2 Cost recovery Initially CWSA policy for the small towns made it clear that water tariffs would have to cover all the operations and maintenance cost, but was not explicit on the recovery of capital expenditure (CWSA, 2001). The new policy indicates that, after the initial community contribution, water tariffs should cover operations and maintenance, major repairs, replacements, and extension to new areas (CWSA, 2003b). However, the operations and maintenance guidelines also states that for total rehabilitation of existing system components cost sharing arrangement and procurement procedures for new projects would be followed (CWSA, 2003c). The lack of definitions to differentiate between major repairs and the total rehabilitation makes the policy unclear. Furthermore, a blanket policy, which does not consider special cases such as a small town with a rather small population but requiring a complex technology, could worsen the plight of some communities with respect to the achievement of public health benefit. 5.3 Interface between “CWSA” and “GWCL/urban” small towns’ water supply In addition to small towns’ water supply being facilitated by CWSA and there are small communities in the urban areas that receive service from the urban public utility (Ghana Water Company Limited, GWCL) as part of urban water supply. The potential transfer from “CWSA small town” to GWCL small town” and vice versa, raises the following


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questions (Sarpong Manu, 2001): Whose prerogative is it to make this decision—MWH, DAs or the WSDB?, What will be the criteria for any such transfer? At the moment a small town (Ejisu) with a population of about 15,000 but under GWCL supply service areas wants to come under CWSA and benefit from the small towns facility. They claim that for the past 15 years water supply from the urban water supply utility has been basically non existent.

6 CONCLUSION AND RECOMMENDATIONS At the national level the institutional linkages and the accountability mechanisms between MLGRD/DAs, CWSA, MWH and the Water Resources Commission (WRC) are weak. This results in ineffective monitoring and management of the small towns’ water system as well as the water resources. At the district level the DWSTs members seconded from the other department does not make the DWSTs permanent in the DAs structure affecting delivery of water services. The policy on cost recovery is not clear especially on the recovery of capital expenditure such as rehabilitation and major replacement. Based on the conclusions, the following recommendations are made: ● At the national level there is the need for a closer collaboration between CWSA, MWH, WRCand MLGRD through the inter-ministerial coordination and at the regional level DAs, RCC and CWSA (regional office). In addition there is the need to include accountability mechanisms in the Memorandum of Understanding (MOU) between the DAs and CWSA. ● The Government of Ghana should speed up the process of establishing the Works Department within the DA to strengthen the DWST position in the DA. ● CWSA should clarify the policy on cost recovery. Where there is room for subsidies, the source of the subsidy and criteria for eligibility should be made explicit.

REFERENCES Arthur, E. 2002. Manpower survey at the district assembly and community levels for small towns’ water supply.. BSc Thesis, Kwame Nkrumah Univ. of Science and Technology, Kumasi, Ghana. Asamoah, K. 1998. Ghana: The Community Water and Sanitation Project. Paper presented at the Community Water Supply and Sanitation Conference at the World Bank, Washington, DC. CWSA, 2000. The Project Operational Manual (POM) of CWSP-2, CWSA: 10–11. CWSA, 2001. Small Towns Water supply and Sanitation Policy, CWSA. CWSA, 2003a. Investment Opportunities in the Community Water and Sanitation sub-sector. A presentation to an Americo-German Investors in Ghana, CWSA, pp 2, 8. CWSA, 2003b. Small Towns Water and Sanitation Policy. Community Water and Sanitation Agency, Ministry of Works and Housing, Government of Ghana. CWSA, 2003c. Small Towns Water and Sanitation Policy. Operation and Maintenance Guidelines. Community Water and Sanitation Agency, Ministry of Works and Housing, Government of Ghana. GOG, 1993. Act 462, Local Government Act, Ministry of Local Government and Rural development. Government Printer, Assembly press, Accra.


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GOG, 1998. Act 564, Community Water and Sanitation Agency Act, 1998. Government Printer, Assembly press, Accra. Jonah, E. 2003. Performance Assessment of Small Towns Water Supply System: The role of management models an institutional structure, MSc Thesis, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana. MWH, 1999. WATER. Comprehensive Development Framework. Ministry of Works and Housing, Ghana. Nyarko, K.B. 2000. Ghana Water and sanitation sector: Drivers for water performance. PhD Proposal, IHE Delft, The Netherlands. Sarpong Manu, K. 2001. PPIAF/CWSA PSP in Small Towns Water Study. CWSA, Sept 2001. WDI, 2002. World Development Indicators, http://www.worldbank.org/data/dataquery.html

Socio-economic performance of Sepeteri irrigation project in Nigeria O.O.Olubode-Awosola & E.O.Idowu Department of Agriculture Economics, Obafemi Awolowo University, IleIfe, Osun State, Nigeria Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: This study tried to assess the economic, social and financial viability of irrigation the project and examine the efficiency of resource use among the project farmers. Data from all the Sepeteri Project’s farmers during the 2001/2002 seasons were used. Factor share approach was used to examine the resource use efficiency among the farmers. Records of the project’s activities from 1995/96 to 2001/2002 seasons were summarised to some socio-economic performance indices. All the farmers perceived irrigation fee cheap however, 77% attributed their low demand to lack of credits. The irrigation service was acceptable to the farmers with ease of collection. About 67% of farmers do not accept responsibility of making the project a success. Farmers were not efficient in resource use. It was concluded that while the irrigation fee is far below its economic value, it is high enough for the farmers and this prompts them to prefer rain-fed to irrigated cropping. The project was not financially viable due partly to insufficient funding and low level of demand from farmers.

1 INTRODUCTION Up to 1960s, Nigeria was almost self-sufficient in staple food crops from the relatively abundant rainfall. However, from the 1970s, the long drought; the resulting recurrent desert encroachment and the substantial rate of increase in population brought set back Nigeria’s agriculture. The emergence of these three phenomena necessitated public investment in formal irrigation. Irrigation involves development of water resources, conveyance and distribution of water supply at the field coupled with necessary water management exercises (Chukwuma 1993). River Basin and Rural Development Authorities (RBRDAs)’ Irrigation projects were established between 1973 and 1979 to cover every part of the country. They were to carry out a number of functions particularly the development of irrigation infrastructure in their respective areas of operation. Consequently, thousands of tons of crops such as tomatoes, groundnut, wheat, cotton,


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millet, maize, etc, were grown by small-holder and commercial farmers. However, the overall performance of the existing irrigation facilities had been on a decline owing to a combination of technical, socio-economic and institutional factors (Nwa 1993). The projects are saddled with inadequacy of untimely funding (Akinkoye 2001) hence, not self-sustained. Consequently, the 1995–97 Corporate Plan mandated RBRDA to generate funds internally to cushion the dwindling funds from the budgetary allocations in order to meet substantial portions of their recurrent costs. Ordinarily, a guided increase in agricultural commercialization leads to increase in purchase of farm inputs, scale (farm size) and specialization in farm enterprises and changes in the role and nature of farm labour inputs. However, this move, if not guided, has the tendency to expose the RBRDAs to been more concerned with the activities that return highest internally generated revenue and possibly less concerned with meeting the irrigation needs of the intended beneficiaries is vital. To this end, while most research efforts on improving the performance of public irrigation projects have focused on the structure, technology and environmental issues, this research focused on social and economic performance of the system as well as the resulting effect on its sustainability and achievements of its statutory functions in the face of commercialization and eventual privatization. The broad objective of this study is the assessment of the socio-economic performance of Sepeteri Irrigation Project. The specific objectives are to: i. Examine the socio-economic characteristics of the farmers; ii. Examine the factors that affect demand for and supply of irrigation services in the project area; iii. Assess the economic, social and financial viability of the irrigated cropping and; iv. Determine the efficiency of resource use among the irrigation project farmers.

2 CONCEPTUAL FRAMEWORK Farmers are primarily concerned with the profitability of their enterprises at individual farm levels. Hence, economic performance of irrigation project farmers is based on a production function and viewed in terms of the efficiency with which farmers combined irrigated plot with other resources such as labour, fertilizers, etc., in the context of institutional framework and management practices of irrigation projects. Farmers are expected to meet economic optimum criteria by adjusting inputs and outputs to relative prices. According to the concept of marginal productivity, a rational producer allocates each variable input according to its market price. This concept is supported by the theory of equilibrium in factor markets under profit maximization, which requires that a factor input be paid its value of marginal physical product (VMP). If a factor is paid higher than its VMP, it is over-utilized and if otherwise it is under-utilized (Henderson & Quandt 1980). However, public irrigation projects in developing nations like Nigeria usually do not meet the conditions for competitive market analysis as explained above because its outputs are natural resources (i.e. land and water), which are developed for national economic efficiency and development. According to Schreiner et al. (1989), such a project is characterized by concepts like natural monopoly, derived demand, etc.

Socio-economic performance of Sepeteri irrigation project in Nigeria

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Therefore, it is quite possible for project to record negative returns to the agency management because of high cost of capital, yet farmers are expected to make profit consistently. Therefore, rational irrigation policy should ensure that the only sound reason for fixing irrigation fee is the net additional benefits it offers. These benefits accrue to the region and the society as a whole. The major impact of these benefits is to be found in land use, employment, cropping pattern, farm inputs, etc. So, priorities are always given to these benefits above financial returns accruing to the government from irrigation fees. 3 LITERATURE REVIEW 3.1 The state and roles of irrigation projects in Nigeria’s agriculture The practice of irrigation in Nigeria dates back to 700AD. Formal irrigation scheme started in 1926 in Kware, Sokoto State. Subsequently, an irrigation policy for the Northern Nigeria was promulgated in 1963 to construct village-level irrigation schemes. Studies were then conducted to examine the water resources and irrigation development potential in Nigeria. The productivities of Sokoto-Rima and Chad Basin Development Authorities established in 1973 were huge and impressive (Adegbola & Akinbode, 1986). The then Federal Military Government established nine (9) more RBRDAs by 1976 to promote irrigated agriculture in order to enhance food self-sufficiency programmes (OORBRDA 1998). Sepeteri Irrigation Project is a farmer-based irrigation project under the Ogun-Oshun River Basin and Rural Development Authority (O-ORBDA), a parastatal of the Federal Ministry of Water Resources and Rural Development. Consequent to the commercialization programme and the addition of rural water supply function, the River Basin Development Authorities (RBDA) became River Basin and Rural Development Authorities (RBRDAs) since January, 1995. Through the RBRDAs, a number of hectares of lands were available under irrigation. However, the sustainability and efficiency of these formal irrigation projects have started to decline. To arrest this situation and to further explore irrigation potentials, corporate farmers, State’s Agricultural Development Projects (ADPs), private organizations and local governments started investments in small-, medium-scale irrigation projects. Despite these efforts, the various irrigation systems developed so far have not regained the initial performance especially production of import-substitute and export crops. Research findings showed that the productivity of the existing irrigation schemes is on the decline as a result of a combination of technical, social, economic, institutional and political factors (Kolawole 1988). 3.2 Empirical irrigation project performance evaluation The conscientious definition of irrigation performance was reiterated by Bos (1997) as a measure of the degree at which irrigation agent responds to the irrigation needs of its farmers and the efficiency with which the farmers use the resources. Omezzine & Zaibet (1998) used both allocating and irrigation efficiencies as indices of modern irrigation performance in Batinah Region of Oman to examine the economic and technical


290

efficiencies respectively. Both revealed inefficient water use. The report is that size of irrigated farms and unit cost of water are factors to be considered in the studies of water use and management. Mandal et al. (1995) in an attempt to examine resource use efficiency with respect to farm size of Irrigated HYV Boro Rice Cultivation in Mymensingh District of Bangladesh used factor share approach by estimating a CobDouglas production function. The study revealed that no farm size group allocated resources efficiently. 3.3 Water pricing and irrigation project performance Moore et al. (1994) in a study of four regions of the Western United States discovered that farmers respond to increase in water price by shifting to crops that require less volume of water, hence reduction of acreage of crops requiring high volume of water. This implies that levying too high a charge results in under utilization of facilities such as has occurred on the Sarda Canal in India (NCAER 1959). However, Krishna (1963) found that increase in general water rates would no doubt increase the technical efficiency with which water is applied. It is observed that water abstracted and lifted to field level from wells by human or animal power or by pumps at high private cost, is utilized with much greater efficiency than cheap government canal supplies. Kwanashie et al. (2000) investigated the extent to which poor pricing, poor planning, lack of good management and poor project monitoring and evaluation have affected water resource use in Nigeria. They studied Bakalori Irrigation Project in Nigeria and concluded that these factors undermined water resource management in Nigeria. They then recommended market-based strategies for allocating water between competing users for efficient and cost effectiveness. 4 METHODOLOGY Sepeteri Project is one of the O-ORBRDA’s Irrigation projects supplying irrigation services up to 2001/2002 cropping periods. O-ORBRDA has seventeen (17) farmer-based irrigation projects. However, only two (2) Sepeteri and Itoikin still supplied irrigation services as at 2001/2002 cropping periods. The Sepeteri Project is located in the SakiEast Local Government Area of Oyo State. This is a typical agrarian community. The project was then purposively selected for the study. The project was planned to irrigate 2000ha with sprinkler system. It has 2 dams—Sepeteri I and Sepeteri II of 2.1mcm and 1.3mcm storage capacities respectively for the production of dry season vegetables and Okro. Primary and secondary data were used. One set of structured questionnaire was used to purposively collect primary data from all the forty-four (44) project farmers. They all cultivated a total of 22.35ha. Cross-sectional data of the farming activities during the March 2001 to October 2001 rain-fed cropping period and the November 2001 to March 2002 irrigated cropping period were collected. Secondary data were also obtained from the project records for the periods of 1995/1996 to 2001/2002 cropping seasons. Descriptive and inferential statistics were used to summarize the distribution of data on respondents’ socioeconomic characteristics and factors affecting the supply of


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irrigation service. Index numbers were used to summarize series of figures over years. The indexes show how much one-year figures differ from another. Usually, a fairly typical year’s figure is taken as a base year figure and others are compared to the base year’s figure. The commonest application of index numbers is in comparison of a series of annual figures. In this study, 1995/96 irrigation season was taken as a base year such that subsequent figures were compared with 1995/96 figures. This year was chosen as a base year to examine how fare have the projects been performing in irrigation services since commercialization move in 1995. This year was assumed to be a logical base year for evaluating performance of a previously public irrigation project. To observe the average annual percentage change over the years, the average annual percentage change was computed as follows: (1) where Indexi=base year Index; indexl=last year index and n=number of years over which the trend is studied (Harper, 1991). To examine the performance of the irrigation projects, performance indices according to Bos (1997) were used. The indices used included Fee Collection Performance, Relative Water Cost, Users Stake in Irrigation System, Financial Self-Sufficiency and Relative Cropping Profit Indices were used to assess the operational and strategic performances of the project management agency. The indexes are specified below: (2) where Irrigation fees collected=total revenue collected on irrigation service during an irrigation season

and Irrigation Fees Due=total revenue collectible on irrigation

service during an irrigation season . The Fee Collection Index reveals the level of acceptance of irrigation delivery as a public service to the farmers i.e. the ease of enforcement of irrigation fee or how affordable the fee is among the intended beneficiaries. (3) where Number of Active project farmers=number of farmers in attendance and Total number of project members=number of project farmers informed and expected to be in attendance. Users Stake in Irrigation Project Index reveals the social capacity of intended beneficiaries and organization in managing and sustaining the project i.e. the level of acceptability of responsibility in making the project a success. The “activeness” of members were quantified using acquired data on the attendance of farmers during the last five consecutive regular meetings called by the management for an agreed upon task such as water distribution, conflict resolution, plot maintenance, etc. (4)


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where Actual Income=Total internally generated revenue from irrigation related services and Total MO+M Expenditure=total expenditure on irrigation related services. Financial Self-sufficiency Index reveals the financial viability of the project. (5) where Irrigation Cost per ha=cost of irrigation service per ha (

) and Total

production cost per ha=average total cost of irrigated cropping ( ). Relative Water Cost Index reveals the tendency of farmers abandoning or continuing with irrigated cropping. It is computed on the average. However, The Relative Water Cost Index is perceived to be inadequate to measure the tendency of the farmers abandoning or continuing with irrigated cropping since for some farmers in the developing nations, ends justify the means i.e. (Alimi, pers. comm.) they consider profit far more than the cost. It will then be modified to incorporate the ends, profits from irrigated and rain-fed croppings as specified below: (6) To determine the efficiency of resource use by the respondents, Ordinary Least Squares (OLS) technique was used to estimate parameters of explanatory variables in the postulated Cobb-Douglass production function. The marginal values of inputs used were computed indicating the proportion by which value of crop output changed with one per cent change in the quantity of each input when the quantities of other inputs were kept constant. The production elasticities of the inputs were added together to obtain the returns to scale indicating the proportion by which value of crop output changed with one percent change in the quantities of all the inputs. It is assumed that the value of output depends on level(s) of input(s) such as land, labour, capital and management used and that the production function is a one-equation model (Ogunrowora et al. 1979; Omotesho et al. 1993; Ayanwale 1995). Thus the production function for project farmers was specified as follows: Y=f(X1, X2, X3, X4, u) (7) where Y=Total value of crop output

; X1=size of irrigated farm plot (ha);

X2=expenses on fertilizer and other agro-chemicals ; X3=number of farm household members that assisted in farming activities (man-day); X4=amount spent on hired labour and u=error term. Crop output (Y) was measured in monetary term because two crops—Vegetable (Amaranth sp.) and Okro (Abelmoscus esculentus) were grown together without measuring for sale in standard unit like kilogram. The log-log stochastic production function was fitted for the respondents’ values of crop outputs as follows: ln Y=ln α0+α1 ln X1+α2 ln X2+α3 ln (8)


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X3+ln α4X4 where ln α0 is the regression constant and ln αi is regression coefficient of Xi. The condition of optimum use of inputs as postulated by the theory of equilibrium in factor market under profit maximization is given by the equation: VMPi=MPPi×Py (9) where VMPi=value of marginal physical product from using additional unit of input Xi; MPPi=marginal physical product from using additional unit of input Xi and Py=market price of the output. So the Allocating/Pricing Efficiency Index is given as (10) where MICi=marginal input cost of input i. (i=1, 24). a priori, the expected signs of the explanatory variables are positive. 5 RESULTS AND DISCUSSION 5.1 Respondents’ socio-economic characteristics Table 1 reveals that about 57% of the farmers are indigenes of the project village. The rest 43% are of distant origin. Almost all the respondents, (95%) resides within the project village. This

Table 1. Summary of socio-economic characteristics of respondents. Characteristic Village of origin: Project/Neighbouring villages *Distant villages Village of residence Project/neighbouring villages *Distant villages Age: 21–30 31–40 41–50 Above 50 Sex: Male Female Level of formal education:

Frequency

% Frequency

25 19

56.82 43.18

42 02

95.45 04.55

04 19 13 08

09.10 43.20 29.50 18.20

40 04

90.90 09.10


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No formal education 07 15.91 Primary education 16 36.36 Secondary education 18 40.91 Vocational studies 03 06.82 Years of farming experience: 5–10 10 22.73 11–20 18 40.91 above 20 16 36.36 Year of project participation: 3–6 16 36.40 6–10 23 52.20 above 10 05 11.40 Nature of farming occupation: Full-time 05 11.36 Part-time 39 88.64 Factors affecting size of irrigated plot demand: Credit availability 34 77.27 Cost of irrigation plot in high 05 11.36 Other non-farm engagement 04 09.09 Others 01 02.27 *These are villages farther than 50Km away to Sepeteri, the project village.

revealed that the indigenes within the Project area participated well in the project. About 73% of respondents were within age bracket of 31 and 50 years while about 18% are above 50 years. Also, women scarcely participated in the projects. About 91% of farmers were male. The reason may be that the community is a typical agrarian community where men are predominantly engaged in farming and women engage in other economic activities or assist the male household heads in farming operations. About 16% had no formal education while none had tertiary education, while 77% had between primary school and secondary school education. All the Project farmers had above 5 years of farming experience. In fact, about 37% had above 20 years of farming experience. This result justifies locating the project in the area to help agricultural development and also support the tenet that land should be allocated to farmers with proven commitment to farming as a career. In the same vein, the project farmers had long years of participation. Above half had been with the project for over 6 years. However, few (about 11%) of farmers were full-time farmers. Majority, 88.6% were involved in other economic activities. About 77% acknowledged credit availability as


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*Table 2. Farm specific characteristics of the project and factors affecting supply of irrigation services. Characteristic

Description

Irrigated plot cost (irrigation fee)

–

3300 per ha and collected after marketing of produce

Upland cost

–

Operation problems

– – – – –

800 per ha and collected after marketing of produce Insufficient resource provision Deterioration of physical structures Inadequate finance Lack of tractor and equipment Occasional invasion by Fulani cattle nomads Harsh harmattan between January and February Monkey pest invasion by February Fuel shortage for water pumping Break down of vehicle to transport produce to market Lack of ready markets for produce Electricity failure for pumping irrigation water 4 months (usually between January and April) Implementation committee comprising of project agents and farmers

Management constraints

Other risks and problems peculiar to the project

– – – – – –

Irrigation period

–

Who is responsible for water – allocation * Response from the project staff.

limiting factors of irrigated plot size while 11% perceived irrigation service fee as high while others expressed engagement in other activities as a constraint. 5.2 Factors affecting delivery and supply of irrigation services Table 2 shows some of the farm characteristics and factors affecting supply of and demand for irrigation services in the project. There is crop restriction to vegetable and Okro. The irrigated and upland costs were 3300 and 800 per ha per cropping season respectively and were constant over years. There was no coordinated Water Users Association but the project manager and farmers met occasionally as matter arose especially to allocate land. The project often witnessed inadequate finance, breakdown of tractor and occasional invasion by Fulani cattle nomads. The physical structures are deteriorated. The irrigation period was usually between 4 months of January and April each year. Some risks and peculiar problems that usually discouraged project participation included harsh harmattan between January and February each year, monkey pest invasion by February each year and lack of ready markets for the produce.


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5.3 Socio-economic and financial performance of the project Table 3 reveals that the average irrigation fee collection performance index is 96%. This implies ease of enforcement of irrigation service charge i.e. despite the payment is allowed until after marketing of produce. The User’s stake performance index is 67%. This may be interpreted to mean that about 67% of the farmers were actively involved in the last five (5) obligations required of them for running the project. However, the performance declined at an average rate of 8%. Average Financial self-sufficiency index is 29%. This implies recovering about 29% of the expenditure on the irrigation services rendered to farmers. This implies decline in costs recovery at the annual rate of 25%. Cost of irrigated plot as a percentage of total cost is 20%. This is not much different from 18% reported by Mandal et al. (1995) among irrigation farmers in Mymensingh area of Bangladesh. However it should be noted that the percentage of irrigated plot cost to total production cost is high enough to make farmers abandon irrigated for rain-fed cropping because most mentioned lack of credit facility as a limiting factor to demand for irrigated plot. Besides, the ratio of profit from irrigated cropping to profit from rain-fed cropping is 1.08. This implies that there is no statistically significant difference between profits to irrigated and rain-fed croppings.

Table 3. Socio-economic performance indices of the project. Index Fee collection Users’ stake Financial selfsufficiency Relative irrigated plot cost (as a % of total cost) Relative cropping profit

Average index (%)

Average annual % change in index

96 67 29

4.3 −8 −25

20

1.08

Table 4. Estimates showing efficiency of resource use from the 2001/2002 irrigated cropping. Variable

Average Regression VMP coefficient

MIC

Dependent variable: Y 41,569.91 Explanatory variables: Intercept – 10.67 – – – 0.51 0.718*(4.55) 58,686.93 3300 17.78 X1 1900 0.069 (0.89) 3.16 1900 0.00167 X2

Elasticity of production

– 0.72 −0.069


X3

1.0

X4

500

−0.078 −648.49 500 −1.30 (0.44) −0.094 −1.90 500 0.0038 (0.51)

297

−0.078 −0.094

Other statistics: N=44 R2=0.39 F=5.79* Return to scale=0.62 *Significant at 5%.

5.4 Efficiency of resource use among the respondents From Table 4, 39% of variability in the value of output was explained by the set of explanatory variables captured in the model. The 5.79 F-statistic is statistically significant at 5% level indicating that joint effect of these explanatory variables is significant. The coefficient of irrigated plot size is positive and statistically significant at 5% level. The coefficient of amount spent on chemical has positive sign but not significant. This implies negligible increase in output value results from additional unit increase in the amount spent on chemicals. The coefficient of family labour is negative and not significant. This implies additional use of family labour brings about decrease in output value. This is contrary to expectation and may result from cultivating too small a plot. Coefficient for hired labour is negative and insignificant. This implies that additional use of hired labour results in decrease in output value. The regression constant is 10.67. This is positive and implies that on the average farmers are technically efficient in realizing as much as 11 times in value of input used. This agrees with result reported by Ogunfowora et al. (1979), Omotesho et al. (1993) and Ayanwale (1995). However, the farmers were not efficient in resource allocation. The values of marginal physical products are far different from corresponding marginal input costs (MIC). VMP of irrigated plot is much higher than MIC of irrigated plot. This implies there is scope to increase irrigated plot size to generate higher income. The small and or negative ratios of VMP to MIC of other inputs imply they were over utilized in combination with irrigated plot. Also, the return to scale is 0.62. This indicates decreasing return to scale that the farmers operating under irrational zone of production. 6 CONCLUSION In conclusion, there is higher level of participation from the neighbouring villages to the project. They were mostly resident farmers. Also, they were mostly male with low level of formal education but they had long years of farming experience and project participation. Majority was aged between 31 and 50 years and above. Most of them were part-time farmers and attributed their small level of irrigation participation to lack of


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credit facility. Inadequate funding and deteriorating structures hindered the level of irrigation supply of the project. The performance indices revealed that the irrigation service is acceptable to the intended beneficiaries. Higher cost per hectare of irrigated cropping connotes tendency among the farmers to abandon irrigated cropping for rain-fed cropping. However, the farmers do not accept responsibility of making the project a success. The project is not financially self-sufficient partly for insufficient funding for operations and partly low level of demand from farmers. The farmers were inefficient in resource use. The results call for reform in management of irrigation system such that privatization efforts should not tie down peoples’ land unused; Specifically farmers should be encouraged into coordinated and recognized WUA that incorporate credit lending and efficient marking. Further research should look at ways to rationalize family labour. In the same vein, on hired labour other means of bargaining should explored. REFERENCES Adegbola, A.A. & Akinbode, I.A. 1986. A review of old and current agricultural development schemes in Nigeria: Lessons for future programme designs. In Agricultural Development in Nigeria. Ife Journal of Agriculture special publication, 8:1–34. Akinkoye, O. 2001. An overview of organization and management of public sector irrigation schemes. Paper presented at the National Workshop on Participatory Irrigation Management organized by National Agricultural Extension and Research Liaison Services (NAERLS), Ahmadu Bellow University, Zaria in collaboration with the Department of Irrigation and Drainage, Federal Ministry of Water Resources, Abuja. 26–30 March 2001:12pp. Alimi, T. (Personal communication). Ayanwale, A.B. 1995. Resource use efficiency in cassava processing in Oyo North Area of Oyo state, Nigeria. Ife Journal of Agriculture 16, 17:123–135. Bos, M.G. 1997. Performance Indicators for irrigation and drainage. Irrigation Drainage Systems 11(2): 119–137. Chukwuma, G.O. 1993. Some Considerations in Developing Irrigation Research Priorities for Nigeira. Proc. National seminar on Irrigation Research Priorities for Nigeria held at the University of Ilorin, Nig. 20–23 April 1993:65–71. Henderson, J.M. & Quandt, R.E. 1980. Microeconomic Theory: A mathematical Approach 3rd ed., McGraw-Hill Kogansha Ltd. Japan, 420pp. Herpar, W.M. 1991. Statistics, London, Pitman Publishing: 501pp. Kolawole, A. 1988. RBRDAs and vulnerability to hunger in Nigeria, the case of the South Chad Irrigation Project. Food Policy 13(4):389–396. Krishna, R. 1963. Farm Supply Responses in India-Pakistan: A case study in the Punjab Region: Economic Journal, Sept, 1963. Kwanashie, M.A., Togun, A., Ajobo, O. & Ingawa, S.B. 2000. Nigeria Water Resources Management Strategies—Economic and Financing. Technical Report, 16pp. Mandal, K.C., Sabur, S.A. & Molla, A.R. 1995. Resource use efficiency of irrigated HYV boro rice cultivation by difference farm size groups and its impact on employment and distribution of income in DTWII project area of Mymensingh Bangladesh J. Agric. Econs, 8(1):71–87. Moore, M.R., Gollehon, N.R. & Carey, M.B. 1994. Multi crop production decisions in western irrigated agriculture: the role of water price, American, Journal of Agricultural Economics, 76(4):859–874. NCAER (National Council of Applied Economics Research) New Delhi 1959. Criteria for fixation of water rents and selection of irrigation projects, London, Asian Publishing House.


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Nwa, E.U. 1993. Irrigation Research Priorities for Nigeria. Proc. National Seminar held at the University of Ilorin 20–23 April, 1993, Ilorin, Nigeria, Nwa, EU, Pradhan, P. (eds) IIMI, 104pp. Ogunfowora, O., Esang, S.M. & Olayide, E.O. 1979. Resource productivity in traditional agriculture: a case study of four agricultural divisions in Kwara State of Nigeria. Journal of Rural Economics and Development 9(2):119–131. Omezzine, A. & Zaibet, L. 1998. Management of modern irrigation systems in Oman: allocative vs. irrigation efficiency. Agricultural Water management, 37(2):99–107. Omotesho, O.A., Olufe, J. & Oladeji, S.O. 1993. Resource productivity in food crop production in some selected villages of Oyi Local Government Area, Kwara State, Nigeria. Ife Journal of Agriculture 14(15): 90–97. O-ORBRDA 1998. Federal Republic of Nigeria, Ogun-Oshun River Basin and Rural Development Authority 1997 Annual Report, January, 1999. 49pp. Schreiner, D.F., Badger, D.D., Welsh, M.P. & Suprato, A. 1989. Policy Applications in Natural Resource Projects. In Agricultural Policy Analysis Tools for Economic Development (ed) L.Tweeten, London, Westview Press, 279–321.

Theme D: Application of geophysical, GIS, and remote sensing techniques

Mapping vegetation for upscaling transpiration using high-resolution optical satellite and aircraft images in Serowe, Botswana Y.A.Hussin1, D.C.Chavarro1, M.Lubczynski1 & O.Obakeng1,2 1

International Institute for Geoinformation Science and Earth Observation (ITC), Enschede, The Netherlands 2 Geological Survey of Botswana, Lobatse, Botswana Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: High spatial resolution images of multi-spectral digital TETRACAM camera were used to map vegetation for upscaling transpiration from tree-bush-shrub of Serowe, Botswana. The camera was mounted on a small aircraft to collect data in 30, 60 and 100cm spatial resolution. The results were compared with one-meter improved multispectral IKONOS satellite images. The high resolution airborne images show high potential for mapping tree-bushy-shrubby vegetation of the study area for up-scaling transpiration. The spectral characteristics of the high spatial resolution images are similar to IKONOS satellite images, while the spatial characteristics of the high spatial resolution images are much better than the one-meter MS IKONOS satellite images.

1 INTRODUCTION As part of the water cycle in the nature or what is well know as the hydrological cycle, surface water is heated by solar radiation and thus evaporated to the atmosphere. However, water in plant is emitted through leaves by a process called transpiration. Vegetation cover is a major component of the hydrological cycle. It has influence on the hydrology of both ground and surface water and on soils. The illogical use or abuse of natural vegetation can have a major effect and consequently changes the hydrological cycle and produce adverse effects. These effects can be very dramatic in arid and semiarid regions. In these regions the climate is very sever with extremely hot temperatures up to 50°C and high evaporation and low annual rainfall. In Botswana, just like any other semi-arid country, water is scarce and surface water is available only for short periods after the rainy season. The main water supply is groundwater. Vegetation in Botswana, as

Mapping vegetation for upscaling transpiration

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in any other semiarid ecosystems, is often characterized by tree-bush-shrub-grass savannas and woodlands. The increasing demand for fodder and fuel wood has led to drastic declinations on the vegetation cover. The transpiration from vegetation is contributing to the development of cloud cover and consequently to the precipitation. Thus, the amount of ground water is related to the vegetation cover. Research work in Botswana have proven the assumption that water loss comes from plants relies under the experience of rooting plant systems depth for (68m) Le Maitre et al. 2000. The transpiration measurements where done during dry season were soil evaporation was almost negligible. Accurate ground transpiration estimates become more important being the connecting link between groundwater balance and transpiration model from plant. Therefore, a relationship can be established between the ground water and the biophysical parameters of vegetation cover. Accurate mapping of vegetation cover would lead to assessment of the biophysical parameter of vegetation and consequently to transpiration. The objective of this paper is mapping vegetation cover for up-scaling transpiration using high-resolution optical satellite (IKONOS) and aircraft images (TETRACAM). The study area of this research is located in Serowe, Kalahari, Botswana. 2 VEGETATION MAPPING WITH REMOTE SENSING Forests cover large areas of the global land surface. For many developing countries, it represents an important income source for their economies. Due to over exploitation, forests are currently under constant risk. The protection of forests from disasters (e.g. fire, disease, erosion, deforestation, over grazing) over extensive area is difficult without having any information such as condition, area, species, age classes and volume. With these types of information, it is possible to make a proper management of the forest by identifying and selecting the appropriate area for different management purposes, such as, harvesting, protection, etc. Having all these information collected, there is a need to store the referred information properly, for better and comprehensive use. For this reason, forest maps play an important role in organizing gathered information for further strategies and policies determination in order to make the best use of forest. Different approaches for mapping, like land survey, aerial photographs and satellite imagery can be used depending on the level of detail required and the extension of the area under study. For wide areas, satellite imagery has been shown effective for forest classification and consequently mapping. It is recognized that different satellite or airborne imagery can give different results in terms of information extraction. These different results relate to differences in spatial and spectral resolution. Vegetation mapping involves the evaluation of the existing data and information, collecting field data or ground truth, analysing the data and finally developing the vegetation map and validate it (USGS, 1994). Riquene (2002) have studied the vegetation condition of the current research area using Landsat-TM images and ASTER Optical scanner sensors. The study concluded that ASTER images resulted in better vegetation map than TM because of its higher spatial resolution of the 15 meter than TM of 30 meter. Further more the results showed that ASTER data gave more


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reliable vegetation maps than Landsat TM data. Mapanda (2003), following the steps of Riquene research, who used high spatial resolution (4 meters) multi-spectral satellite images of IKONOS in comparison with ASTER images of 15 meter spatial resolution, have concluded that IKONOS images gave much better results in mapping the vegetation cover of Serowe, Botswana. This research is going one step further in using higher spatial resolution of multispectral images. These images were acquired using Tetracam multi-spectral digital camera. The camera was mounted on a small aircraft and has collected images in 30cm, 60cm and 100cm spatial resolution. This paper is presenting the first preliminary results of the use of the Tetracam airborne multi-spectral digital images for mapping tree-bushshrub-grass-savannas and woodlands vegetation cover of part of Serowe, Botswana. These images will hopefully be used for up-scaling transpiration of the vegetation in this area in conjunction with IKONOS MS data. 3 STUDY AREA The study area is located in the Central District, about 275km NE of Gaborone the capital of Botswana. Topography is gentle, which varies from 1060 meters above sea level to approximately 1240. It is characterized to be lower in the east and southeast of the region, and the highest location in the vicinity of the escarpment edge. From these ones the average slope is 5% and it gradually decrease to less than 1% towards the east and southeast. Soils units, which can be found in that region, are related to arenosols, regosols, lixisols, luvisols and vertisols. Arenosols are the most common soil units in the study area. It has low moisture retention capacity than the other soil units. Climate is a semi-arid with a mean annual rainfall of 447mm. Rainfall occurs mainly in the summer fallowed by a dry winter season. Summer season stretches from October to April and the winter begins in May to September (Tyson, 1986) (Obakeng, 2000). Main vegetation type is thought that belong to the Northern Kalahari Tree and Bush Savanna. Trees are mostly of Acacia species, which are characterized by the marked tendency to occur in cluster, and are normally accompanied by a variety of grass species such as Ariatida and Eragrotis. Vegetation communities are determined by location on either sandveld or hardveld areas. Dense vegetation is found within and along river courses. This suggests that the vegetation density is governed by the availability of water, which may be partly controlled by topography and geomorphology (Obakeng, 2000). 4 DATA AND ANALYSIS The airborne multi-spectral data was collected using TETRACAM multi-spectral digital camera, which collects its data in three spectral bands namely red, green and near infrared. The data is collected in a rectangular frame of 1280×1024 pixels. The size of the pixels (e.g. ground resolution) would depend then on the altitude of the aircraft above the ground. The camera would saved the image in DCA format (Digital Camera Format), which is a compressed file that can be un-compressed and transferred to Bitmap format


305

that can be imported to any image processing software. The Airborne data was collected in three different spatial resolutions 30, 60 and 100cm. An area of 10×10km was selected as a study site. It is located in the Hardveld part of the Serowe terrain, on which two multi-spectral IKONOS satellite scenes of November 2001 and February 2002 were collected. These images are collected with 4 spectral bands (blue, green, red, and NIR). The spatial resolution of these data sets is 4 meters. A MS image, so called panchromatic sharpen, was available too. The Pan-Sharpen image is a MS image fused with the Panchromatic image of IKONOS, which has 1 meter spatial resolution. Thus the spatial resolution of the new MS image will be improved to 1 meter. For this study area, two aerial surveys were implemented to collect the multi-spectral digital camera data. The first aerial survey was done in November 2003 and the second one was done in February 2004. These surveys were designed and implemented using Aerial-Photography types of survey. The survey divides the area into flight lines. Within each flight line, images were collected with a front overlap of 20% and a side overlap between flight lines of 20% too. The following data where collected: 1. 30cm spatial resolution: 39 flight lines with a total of 910 images 2. 60cm spatial resolution: 21 flight lines with a total of 333 images 3. One meter spatial resolution: 14 flight lines with a total of 187 images. A qualitative approach was used in the analysis of airborne multi-spectral digital images, which mainly involves visual interpretation, spectral signature measurements, spatial features measurements and comparisons of different spectral and spatial data resolution. The same approach was used with the MS IKONOS satellite data to be compared to the airborne data. 5 RESULTS AND DISCUSSIONS The results presented in this paper are the first preliminary findings of some exploratory analysis of airborne MS digital images. Supervised classification and accuracy assessment was not done because an organized fieldwork to collect ground truth was not done yet in the study area. The authors are planning for one in early May of this year (2004). A spectral signature analysis of the 30cm, 60cm and one-meter spatial resolution images of the MS digital Tetracam airborne camera using the digital interpretation of the false color composite, unsupervised classification, and Normalized Difference Vegetation Index (NDVI) (Figures 1–6) showed that the sample used has 3 different spectral classes which referred to 3 different species of the bushy vegetation in the area. It also showed two high contrasted spectral classes, which refer to a soil and a grass classes the selected sample shown in the mentioned figures. A comparison of the above findings with the same signature analysis to the MS IKONOS image of improved one-meter spatial resolution showed similar results of 3 spectral classes of the bushy vegetation and two other high contrasted classes representing the soil and grass classes.


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Figure 1. Color composite image of 30cm spatial resolution of MS airborne MS camera.

Figure 2. NDVI map the 30cm spatial resolution of MS airborne image.


307

Figure 3. Unsupervised classification map of the 30cm spatial resolution of MS airborne image.

Figure 4. Color composite image of 60cm spatial resolution of MS airborne MS camera.


308

Figure 5. NDVI map the 60cm spatial resolution of MS airborne image.

Figure 6. Unsupervised classification map of the 60cm spatial resolution of MS airborne image.


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Figure 7. Color composite image of one-meter MS IKONOS satellite image.

Figure 8. NDVI map of one-meter MS IKONOS satellite image.


310

Figure 9. Unsupervised classification map of one-meter MS IKONOS satellite image. Figures 7–9 show the false color composite, unsupervised classification, and Normalized Difference Vegetation Index (NDVI) of the MS IKONOS satellite image. A general comparison of IKONOS images and the airborne MS image showed that both types of images are close in their spectral characteristics, especially the improved one-meter resolution of IKONOS as compared to the 30 and 60cm resolution images of the airborne data. A spatial analysis of several selected objects (e.g. bushes, trees, soil and grass) on the images showed that when spatial resolution increases the accuracy of the information extracted increase. For example a canopy diameter of a single tree measured on the ground is 5.5 meter. The same tree canopy diameter measured on the one-meter, 60cm and 30cm spatial resolution of the airborne MS images are 7.1, 6.13 and 5.38 meter respectively. This is a clear evidence that the higher the spatial resolution of the image the better the accuracy of the analysis or interpretation output. Moreover, the higher the spatial resolution the higher the amount of details extracted from the images as a results of the interpretation or any image analysis technique (e.g. classification or image transformation such as NDVI). For example, some of the tree species in this study area are likely to grow in clusters structure. These clusters may include 3–5 trees in one cluster. On average the crown diameter of these trees say 5 meters. Consequently a total area of the canopies from such cluster may reach up to 125 square meters. The lower the spatial resolution (e.g. one-meter or lower), the less details that represent such a cluster on the image and vis versa. However, in the case of a small bush or shrub, which, has a canopy of approximately one-meter diameter may not show clearly on the image because of the open crown structure. In such a case the spectral reflectance of the soil will dominate such the


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reflectance from the canopy of the bush. While when using higher resolution (e.g. 30 and 60cm) the representation or the appearance of a small bush will be possible. Therefore, as the spatial resolution increase the spatial information extracted about an object on the images (e.g. a bush or a tree) will consequently increase. The information will include the surrounding area (e.g. soil or grass) of the tree or the bush targeted. This means that using higher spatial resolution we can define the size and shape of any tree or bush much accurate than using lower resolution. The size of the crown of a bush or tree is effecting the estimation of the transpiration of that bush or tree. Consequently this will effect the process of up-scaling transpiration from the area in general. As far as the spatial resolution is concern, a general comparison of IKONOS images and the airborne MS image showed that the information extracted from the 30cm and 60cm spatial resolution images of the airborne MS images is much better than the onemeter resolution of IKONOS image. 6 CONCLUSIONS The following conclusion remarks can be drawn: – The high spatial resolution 30 and 60cm multi-spectral digital Tetracam images have high potential for mapping tree-bushy-shrubby vegetation of semi-arid area (e.g. Serowe, Botswana) for up-scaling transpiration. – The spectral characteristics of the high spatial resolution images are similar to IKONOS satellite images. – The spatial characteristics of the high spatial resolution images are much better than the one-meter MS IKONOS satellite images.

ACKNOWLEDGMENT This research work was partly supported by the internal research fund of GWFLUX Project at ITC. However, Botswana Geological Survey (BGS) has offered the main financial support of the aerial survey missions, fieldwork logistics and transportation. The authors appreciate and acknowledge the support of Botswana Geological Survey. REFERENCES Le Maitre, D.C., Scott, D.F. & Colvin, C. 2000. Information on interactions between Groundwater and Vegetation relevant to South African Conditions: A review. Groundwater: Past Achievements and Future Challenges, Silili et al. (eds). Balkema, Rotterdam, 959–962. Mapanda, W. 2003. Scaling-up and Mapping Transpiration Using Remote Sensing and GIS: A Tool for Water and Forest Management. Unpublished MSc, ITC—International Institute for Geoinformation Science and Earth Observation, Enschede. Obakeng, O.T. 2000. Groundwater recharge and vulnerability: A case study at the margins of the south-east Central Kalahari Sub-basin, Serowe region, Botswana. Unpublished MSc, ITC— International Institute for Geoinformation Science and Earth Observation, Enschede.


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Riquene, A.H. 2002. Vegetation mapping in Arid Zones: A multi-sensor analysis, the relationship between Vegetation Distribution and Environmental Factors: A case study in Serowe, Botswana. Unpublished MSc, ITC—International Institute for Geoinformation Science and Earth Observation, Enschede. Tyson, P.D. 1986. Climatic Change & Variability in Southern Africa. Cape Town, South Africa: Oxford University Press. USGS, 1994, 19 July 2001. Field Methods for Vegetation Mapping. USGS-NPS. Available: http://%20biology.usgs.gov/npsveg/fieldmethods/ [2001, 24 August 2001].

Gravity study on groundwater structure in Central Butana (Sudan) K.M.Kheiralla TU Bergakademis, Freiberg, Germany A.E.Ibrahim El Neelain, University, Sudan Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: A number of isolated outcrops of Pre-Cambrian Basement Complex rocks scatter over the central plains of Sudan. In the Butana region, several hills occur prominent landmarks within the predominantly flat clay plains. The solid geology of the Butana plain is rather concealed under a veneer of variable thickness of superficial clays covering over 70% of its total area. The present study was suggested in an effort to delineated and define the mentioned anomaly in more detail and give a reasonable geological and hydrogeological exploration for its existence. Integrated gravity methods and geological feature were applied to achieve the above aims. A total of 200 gravity points were conducted in the study area and they are compile to 275 gravity points acquired, by Sun Oil Company (approximately 2475Km2 were covered in the study area). Gravity data analysis was performed by “GEOSOFT” packages. The result show that the gravity lows is largely attributed to the occurrence of low-density rocks (granite intruded) into the high-density rocks (green schist) of the Butana region. On the other hand the gravity high zones unambiguously coincide with the areas of known shallow Basement Complex. This gravity low is largely attributed to the occurrence of lowdensity rocks (granitic intrusion) into the high-density rocks (green schist) of the Butana region. Thus for it is not unusual gravity measurements in such areas introduced by granitic into country rock of higher densities, to reflect apparently anomalies of typical sedimentary basins. However such ambiguity can be resolved by computation of the second derivative.

1 INTRODUCTION Geophysical prospecting conducted by Sun Oil Company revealed strong negative gravity anomalies in Butana region. It is suggested that sedimentary basins might have caused these anomalies (Ibrahim, 1993; Ibrahim et al., 1996). In the study area the


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anomaly (Around Jebel Mundara) lies partially in the Basement rocks. Therefore this research aims to verify the existence of these anomalies and clearly define their extension. In addition, the study aims at determining the type and the dimensions of the rocks causing these anomalies. The study area lies between the Blue Nile River and River Atbara and occupies the Central Butana area, It is bounded by latitudes 14°60′N and 15°80′N and longitudes 34°00′E and 35°20′E. The study area covers about 10,000km2 (Fig. 1). The study area is generally flat, with a gentle slope to the North. The general altitude of the plain is about 500m above mean sea level (m.s.l). The flat monotony of the plain is occasionally broken by some protruding low to moderately high hills or hill chains, which hardly exceed 200m above the ground surface. The climate of the area is arid to semi arid zone of Sudan, characterized by a short duration of a rainy session in summer (July–September), and along dry season for the rest of the year. The average annual rainfall is about 200mm. Average annual temperature over the Butana area is around 40°C in summer (March–October) and 25°C in winter (November–February).

Figure 1. Location map of Central Butana. Table 1. Geological column for butana region (after Iskander et al., 1993). Formation

Age

Superficial deposits Tertiary volcanic

Quaternary/Recent Tertiary

Gravity study on groundwater structure in Central Butana (Sudan)

EL Burg Basal conglomerates The Basement complex

315

Jurassic to cretaceous Precambrian

2 GEOLOGY OF THE STUDY AREA A number of isolated out crops of Precambrian Basement complex rocks scatter over the central plains of Sudan. In the Butana region, several hills occur and make prominent landmarks within the predominantly flat clay plains. The solid geology of the Butana plain is rather concealed under a veneer of variable thickness of superficial clays covering over 70% of the Butana area. Several metasedimentary sub-parallel belts extend for 10–25km in the form of low to moderately elevated ridges surrounded by Butana clay cover (Iskander et al., 1993). The generalized geological column for Butana region can be summarized as shown in Table 1. The majority of the Basement rocks are concealed under the cover of the Butana clay plain. As mentioned, the structural domain in the area is characterized by northeast trending lineaments (Fig. 2). Exposed structures in the metasediments display complex shearing/faulting and tight folding with dipping axial planes where the axes generally have NE-SW trends and with SW mergence Iskander et al. (1993). 3 GRAVITY METHODS 3.1 Introduction The gravimeter used in this survey is a Lacoste & Romberg gravimeter, model D108, which has calibration constant of 1.0863mGal/div and 200mGal measuring range. A total of 200 gravity readings were measured in the study area following a loop survey, with a spacing of 2km between stations (Fig. 3). An area of approximately 2412km2 has been covered. In addition, about 275 gravity points (approximately 2475km2) acquired, by Sun Oil Company were compiled, in the study.


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Figure 2. Geological map of Central Butana area modified after (Ahmed & Ayed, 1996).

Figure 3. Location of measured gravity points.


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Elevation of the gravity station was determined by Global Positioning System (Garmin II GPS Model 1999), with ±10m accuracy. The Global Positioning System, (GPS) device was used to determine the altitudes of the gravity stations and also for navigation. Control was provided by the available altitude benchmarks in the area and by elevation contour maps of scale 1:100,000, determined by the Survey Department in Khartoum. In addition the altitudes of the previous data (Sun Oil data), were determined by micro barometric altimeter. In gravity measurements effects are produced by sources not directly related to the geological objectives or interest of the study, therefore certain reductions or corrections are necessary to remove these effects. Such corrections include drift, tidal, latitude and elevation correction. This compensates for the earth tides, generated by the complex gravitational interaction on the Earth by the Sun and Moon. These effects are often calculated from table published by Geophysical Journal worldwide. In this work it was done by “GEOSOFT” computer program. 3.2 Gravity data processing 3.2.1 Production of Bouguer anomaly map Presentation of the corrected gravity values is commonly made in the form of contour maps, particularly where the survey has covered a grid of more-or-less evenly spaced stations. Exceptionally, where well-isolated profiles have been surveyed, to obtain crosssectional information on a structure, then the results may be presented in the form of profiles. A sequence of profiles may be shown in stacked form, in proper relative location, on a plan map. In either case, the horizontal scale of the presentation should be inversely related to the distance between the gravimeter stations. Also, the contour interval (mGals) may be inversely related to the scale of the presentation. Software programs are available, by means of which either contour map or profile presentation may be conveniently and quickly made. In this work, gridding was performed by “RANGRID”, program of the GEOSOFT package (GEOSOFT manual, 1989). “RANGRID” produces a minimum curvature grid from data randomly distributed or along non-parallel traverses. The method utilizes different available interpolation options, (e.g. Akima, Cubic etc) to calculate the value of object function at the grid points (original data) that falls within a circle with a given radius centered at the grid points. RANGRID roughly smoothes gaps in the acquired data. In the present study, although data have been acquired along lines, but their irregular points spacing tend to make the gravity data look randomly scattered thus fore they have been subjected to interpolation or gridding process by “RANGRID” which seemed to be a suitable technique (GEOSOFT manual, 1989). The resolution of the produced Bouguer gravity map depends on the choice of the grid cell size, as demonstrated by comparison between the maps shown in Figures (4, 5, and 6), which have been produced by 0.0025, 0.04, and 0.4 cell sizes respectively. To judge on the optimum cell size that resolves the Bouguer gravity map, variations of GB.A has been plotted against corresponding variation of the cell size. It is clearly that no practical displacement (change) has occurred beyond 0.4 cell size. Thus this cell size


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(0.4) is consider as the optimum grid cell size suitable for production of the Bouguer gravity map. Contouring of the observed gravity data was performed by “CONTOUR” program of the GEOSOFT package, whose basic function is to thread contour lines through constant levels, defined in a gridded GEOSOFT data file (GEOSOFT manual, 1989).

Figure 4. Bouguer anomaly map, cell size 0.0025. 3.2.2 Production of the residual map The construction of a residual anomaly map due to local structures is therefore a process by which one removes the regional gravity effects. This task could be performed by numerous methods mentioned in the geophysical literature (Seigel, 1995), however in a broad sense they might be classified into graphical or analytical methods.


Figure 5. Bouguer anomaly map, cell size 0.04.

319


320

Figure 6. Bouguer anomaly map, cell size 0.4. The gravity measurements at surface determine the sum of all effect from grass root down to the earth crust. Therefore gravity interpretation frequently begins with some procedure, which separate anomalies of interest from superficial disturbance or from deep regional effects. Various methods may be elaborated to perform the separation of the anomalies in order to emphasize the important and interesting features and to suppress the others. These methods include the following. 3.2.2.1 Graphical methods The regional is far away from measuring points it is represented by a long wavelength anomaly due to deep structure. The regional is sometimes shown as a straight line as a result of smoothing a X-Y plot or contour map anomalies. The regional (long wavelength) anomalies mainly due to the effect of deeper structure (lower crust, mantle and core), while the residual (short wavelength) anomalies represent the shallow structure (near surface and crust structure) and may be upper part of the mantle. The graphical methods involve estimation of the regional field from profile plots or contour maps. The advantage of these methods is that, control could be provided by the available geological information (e.g. Basement depth), obtained from boreholes in the survey area.


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3.2.2.2 Filtering techniques One of the most important problems in the interpretation of potential field data is to characterize it into different geological structures. The regional one of these methods is the analytical or the filtering techniques were employed which are characterized by: Various methods may be employed to separate anomalies. These include: regional, residual, derivative, low pass filter and high passfilter. However, the selection of the appropriate method depends on the nature of the Bouguer anomalies and the empirical judgment of the interpreter, which is of course vital. On the other hand several of the analytical methods are commonly used for determining the regional and then the residual fields. Griffin (1949), Agocs (1951), Fajklewics (1959), and Abd el Rahman et al. (1983), used in their respective techniques, linear combinations of the average fields on a number of concentric circles of different radii to represent the residual at the common center. The residual field is given by: R= G−Z=G−(ax+by+c) Where, G is the observed gravity, R is the residual field, Z is the regional field, a, b and c are constants. The condition for the above equation is that ∑R2=min These are called residual, but do not posses any relationship with local anomalous mass (Paul, 1967). The only physical significance of this residual is their proportionality to the second vertical derivative value; hence their zero contours coincide with the zero contours of the second derivatives (Nettleton, 1976). Lately dependable method have been introduced by Paul (1967), for computing the second vertical derivatives, consequently the residual determined by the previous method loose much of their significance. 3.2.2.3 Second vertical derivative The second vertical derivative technique was used as a two dimensional filter for interpretation of potential field data (Dobrin, 1976). The second derivatives that have been applied in the present study are the second vertical derivative of the vertical component of gravity. If we used the symbol “g” to denote gravity and choose axes so that Z is vertical downward, then the second vertical derivative is the quantity d2g/dz2. The importance of the second derivative for potential field interpretation arises from the fact that the double differentiation with respect to depth tends to emphasize the smaller, shallower geological anomalies at the expense of larger, regional features (Elkins, 1951).


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Figure 7. Second vertical derivative of gravity anomaly map. On the practical side, the second vertical derivative has its disadvantages as seen on map (Fig. 7), that shows a number of anomalies of no actual existence, but they tend to be an interpretation of contours rather than of observed gravity field. The main objective of applying the derivative in this research study is for the delineation of shallow faults. It is interesting to prove how the regional is completely eliminated by the second or higher vertical derivative. This may be shown as follows:

The condition is that,

∑nCn=0

Hence,

Where, Z0 is the average regional at the canter of a particular grid, the residuals around a circle of radius, “n” on substituting,

is the average of


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Therefore, for the second vertical derivative only the equation is given as

This equation clearly shows that, the regional field constitutes nothing to second vertical derivative value, and thus this derivative represents entirely the residual value only. A profile of second vertical derivative of gravity in a direction outward from the center of a negative anomaly usually shows an outer maximum value minimum value ratio r,

and an inner

Bott (1965). The source of the anomaly may be determined by the

In case of a sedimentary basin r>1 while for a granite batholiths r500

Figure 8. Geo-electrical section of the study area, showing three hydrogeology units. resistivity values. Using gravity model, geo-electrical section of the study area in (Fig. 8) showing three hydro-geological units (Kheiralla, 2001), weathered rocks and weathered rocks underlain by fractured rocks underlie alluvial layer. 6 RESULTS AND DISCUSSION The results of a comparative investigation of drainage and lineament mapping from TM imagery using vertical electrical soundings data are described. Initial results show that the land sat image is most useful for mapping detailed fracture pattern while the combination of vertical electrical sounding technique is helpful in the location of major deep-seated fracture zones. The longer NNE to NE trending feature may be important from a regional hydrogeological point of view, where as the NW trending features are significant in that they intersection the major fault.


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Groundwater occurrence is mainly due to the secondary porosity, such as weathering, joints, fissures and fracture/lineaments. The iso-apparent resistivity contour map (Fig. 7) depicts the horizontal variations in the sub surface lithology of the study area. Figure 7 it is found that the high resistivity zones of more than 50Ωm occur from north-eastern part and from southern part of two interested area. Most of the well located in this zone yield a good quantity of water. Good quantity (more than 90,000m3/yr) groundwater potentials have been identified in the high density of drainage/or lineament zone in Butana region, lineaments intersection are important with well yield than are individual. Assuming that wide variations are not present within a few kilometers, groundwater potential zones have been delineated based on surface lithology, drainage, lineaments/fracture pattern from land sat TM imagery and from electrical resistivity studies (Fig. 9). 7 CONCLUSIONS ● The study of land sat TM images identified a lineament trending NE-SW direction and drainage pattern present in the area. ● Moderate to good yield (40–65*103m/yr) are tapping from weathered zones, good yield (70–90*103m3/yr) are tapping from fracture zones.

Figure 9. Different groundwater potential zones.

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● The area as covered with high alluvial and more fractured zones are providing copious amounts of groundwater. ● Range of resistivities and Expected Yield of different zones are presented in table (2). ● The comparatively high density obtained by lineaments concentration/and or drainage system indicated the presence of groundwater potential zones.

REFERENCES Abd el Ati, H.A. 1993. A base line survey Report on Central Butana. ADS project area-UNDPKhartoum. Ahmed, F. 1968. The geology of the Jebel Qeili, Butana and Jebel Sileitaat-Es-Sufr igneous complex, Nile valley, Central Sudan. Unpublished M.Sc. thesis, Univ. Khartoum. Ahmed, F. & Ayed, M.A. 1996. Applied geophysical and satellite imagery techniques, for ground water studies in Central Butana area; ADS report, 25pp, 10–15. Iskander, W. Ahmed, A A. Mokhtar, A. & Fadle, A.S. 1993. Appraisal of mineral and water resources of central Butana, Eastern region-Sudan ADS report 85pp. Kheiralla, K.M. 2001. Geophysical study on groundwater structure at two localities in Central Butana, Central Sudan. Unpublished M.Sc. thesis, Univ. El Neelain. Waters, P. 1990. Methodology of lineament analysis for hydro-geological investigation. In Satellite Remote Sensing for Hydrology and Water Management. E.C.Barret, Power, C.H. & Micallef, A. eds., New York, Gordon & Breach: 1–23. Way, D.S. 1973. Terrain analysis, a guide to site selection using aerial photographic interpretation, Stroudsburg, Dowden, Hutchinson, Ross Inc. Vail, J.R. & Duggue, J.P. 1986. Bibliography of geological sciences for the Republic of the Sudan. 1837–1985, Center Int. Formation Echanges Geol. Paris, Spec. Publ.

Monitoring and modeling of fluxes on Kalahari—setup and strategy of the Kalahari Monitoring project Serowe study case, Botswana M.W.Lubczynski1 & O.Obakeng1,2 1

The International Institute for Geoinformation Science and Earth Observation (ITC), Enschede, The Netherlands 2 Geological Survey, Lobatse, Botswana Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: The ongoing discussion about the presence and the rates of recharge in Botswana, which constrains groundwater sustainability in the country scale, has led to the initiation of a new recharge project in Botswana called Kalahari Monitoring Project. In contrast to previous attempts this project focuses on temporal flux monitoring by using automated data acquisition systems (ADAS). The framework of that project is discussed on the base of the example of the Serowe study area, located at the eastern fringe of Kalahari, where an extensive monitoring network was installed to provide data for spatio-temporal flux assessment. This network allows measurements of saturated, unsaturated and surface zone fluxes. It consists of groundwater table fluctuation monitoring in 21 piezometers, soil moisture and soil suction pressure monitoring in 7 identical profiles comprising measurements at 0.5, 2, 4, 6, 8m b.g.s., one deep suction pressure profile down to 76m (sensors at 15 different depth levels), transpiration monitoring using 51 sap velocity thermal dissipation probes installed at 9 ADAS locations and monitoring of climatic variables for potential and actual evapotranspiration in 10 towers scattered over the study area. This data is either interpreted directly (rainfall, transpiration) or used in 1-D models to calibrate surface and subsurface fluxes such as evapotranspiration, groundwater evapotranspiration and recharge. For spatial data assessment the remote sensing (RS) method is proposed. The evapotranspiration is obtained with RS solution of energy balance, transpiration by RS upscaling of the sap flow measurements and recharge by RS and GIS modeling. The final integration of spatial and temporal data for spatio-temporal flux assessment is carried out by transient groundwater model calibration with spatio-temporally variable recharge and groundwater evapotranspiration. The aspect of partitioning of tree

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transpiration fluxes into saturated and unsaturated zone is tackled by isotopic depth dependent tracing of groundwater and tree response analysis. The preliminary results of this study indicate already that the net recharge in incidental hydrological seasons can be substantially higher than the average recharge defined by isotopic and chemical methods. In other years however, the net recharge is usually negative due to the typical excess of groundwater evapotranspiration over the recharge, which is mainly due to the substantial role of transpiration in the overall groundwater balance.

1 INTRODUCTION A long lasting debate is continued in Southern Africa, particularly in Botswana, regarding the presence, rates and the nature of groundwater recharge on Kalahari. Based on the completed GRES II project, the Kalahari recharge was defined on average in the order of 5mm/y or less, using hydrochemical and isotopic methods (de Vries et al. 2000). The GRES recharge rates obtained mainly with chemical and isotopic methods provide the long-term average recharge. In groundwater modeling such recharge can only be applied as steady-state flux input, which is justified if the temporal variability of fluxes is low. Otherwise, as it often happens in arid and semiarid countries, models have better setup if fluxes are provided in spatio-temporal manner (Lubczynski 2000, Lubczynski & Gurwin 2004). In Botswana for example, in the wet season of 1999/2000 when many places in Southern Africa experienced incidentally high rainfall, the monitored groundwater table rise indicated recharge values several times higher than 5mm/y stated by GRES II project. In the other years however, when rainfall and recharge (R) were low, groundwater table declined to the stages lower than at the beginning of the hydrologic year. This happened not only due to the lateral groundwater outflow but also due to the groundwater evapotranspiration (Lubczynski 2000). Groundwater evapotranspiration (Eg) consists of two types of fluxes: groundwater transpiration (Tg) representing root groundwater uptake and groundwater evaporation (Cg) representing convective and diffusive water flux originated from groundwater table which evaporates while reaching a shallow zone of a few m b.g.s. Similar flux components, such as unsaturated zone transpiration (Tu) and unsaturated zone evaporation (Cu) are also defined with reference to unsaturated zone. The similarity between Tg and Tu as well as between Cg and Cu makes difficult partitioning of the flux contributions of saturated and unsaturated zone. Such difficulty occurs for example when transpiration is assessed by tree sap flow measurements, which represent the combined effect of transpiration originated from groundwater and from unsaturated zone. The assessment and partitioning of Cg is even more difficult because so far there are no methods of measuring of this component and moreover Cg and Cu can also be confused with the surface evaporation when assessment is made from the land surface. Not only temporal assessment of groundwater fluxes is considered as a problem but also the assessment of spatial variability of fluxes. Very often point data characterizing local behavior of saturated-unsaturated fluxes is available, like from specific chloride


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mass balance measurements or from 1-D recharge modeling, but the method of spatial representation of such data is not well defined. It is an ongoing dispute on what are the best and the most efficient schemas to present point flux information spatially, using interpolation, extrapolation by GIS modeling, stochastic modeling or discrete groundwater modeling? Thus in 2001a complex Kalahari Monitoring research project was established in Botswana focusing on monitoring and modeling of surface and subsurface fluxes. The main objective of this project is spatio-temporal assessment of subsurface fluxes for better management of groundwater resources in Botswana. As study areas three hydrologically different semi-arid locations were selected, Maun area, Localane-Ncojane area and, Serowe area. Maun area represents relatively wet conditions of the Delta Okavango with very shallow groundwater table of only few meters below the surface. Localane-Ncojane area represents the western, driest part of Botswana Kalahari with very deep groundwater table on average 100–150m b.g.s. The Serowe area of ~2500km2 on which this study focuses (Figure 1), is currently the most instrumented and the most intensively investigated research area of the Kalahari Monitoring project. 2 WHY SEROWE AREA AS STUDY AREA? The Serowe study area was selected as target area of the Kalahari Monitoring project following the previous research in the same area delivered by SGAB (1988) and WCS (2000). The latter one included also the numerical groundwater model, after which the present study area boundaries were assumed (Figure 1). The study area consists of two contrasting parts, Kalahari sandveld and hardveld, which have different natural and hydrological conditions. The western sandveld part is elevated as compared to the hardveld along the prominent escarpment feature. This elevation is due to the 60–100m eolian Kalahari sand cover on the western, sandveld part, overlying solid rocks such as Stormberg basalts and Ntane sandstones which in the eastern part outcrop or are covered by thin, 0–5m Kalahari sand cover (Figure 1). The sandveld part slopes gently to the west, is fairly flat and featureless without prominent drainage lines. In contrast, the hardveld part slopes steeper and there is a drainage system of the intermittent streams, discharging water mainly after the heavy showers. The majority of the villages in the study area are concentrated along the eastern edge of

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Figure 1. Serowe study area and its monitoring network. the escarpment where some ten years ago, springs were supplying water for habitants. The escarpment line as well as the drainage lines in the eastern part of the study area where groundwater table is relatively shallow (250

>10

9

Drastic weight, Dw=5 Aquifer media

Drastic weight, Rw=4 Vadose zone material BIF gravel

Gravel, 10 coarse sand Dolomite 9 Dolomitic 8 chert

Sandstone, 7 silstone Quartzite 6 Fractured 5 shales BIF Cherts

4 3

Syenite, granite, rhyolite,

2

10 9 7 5 3 1

Drastic weight, Tw=2 Soil media

10

Chert 9 gravel Gravel, 8 sand, sandstone, sandy gravel Dolomite 7

Weather dolomites Sands

9

Calcretes

7

Chert, 6 dolomite Shale, 5 sandyclay, clay Quartzite 4 Sandy 3 chert

Chert 7 breccias Sandy clays 6

Calcrete

10

2

Dolerite, 1 granite

Drastic

8

Clayey sands 5 Weathered 4 BIF (lateritic soils) Clays 3 Shales

0–0.5 0.5–1.0 1.0–1.5 1.5–2.0 2.0–2.5

1 3 5 7 9

>2.5

10

Drastic weight, Cw=3

Gravels

dolorite Drastic

0–2 2–4 4–6 6–8 8–10 >10

2

Ferruginous Clays 1 Drastic

Spatial assessment of groundwater pollution vulnerability

weight, Aw=3

weight, Vw=5

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weight, Sw=3

T=topography (slope) I=vadose zone C=hydraulic conductivity The DRASTIC score Di is a relative value, with no specific units. A speed sheet program was written to derive the DRASTIC indices for the various boreholes studied. The following table shows the DRASTIC ratings and weights adopted in the study. 5 RESULTS AND CONCLUSION The results indicate that about 47% of the Kanye wellfield area is overlain by soils with high vulnerability to pollution (class 1 soils) Fig. 2a; 44% of the area is overlain by soils of intermediate vulnerability (class 2 soils) and 9% of the area is overlain by soils of low vulnerability (class 3 soils). The geological vulnerability maps (Fig. 2b) show that 40% of the well field area is underlain by rocks with high permeability and significant fracturing thus of high vulnerability (class 1 rocks), 49% of the area is underlain by rocks of medium vulnerability (class 2 rocks) and 11% of the area is underlain by rocks of low vulnerability (class 3 rocks). Considering the overall study area bounded between 25–25.4°E and 22.8–23.5°S, the ground water vulnerability map (Fig. 2c) indicates that 22% of the well field area is very highly vulnerable to pollution, 35% of the area is highly vulnerable to pollution, 34% is moderately vulnerable to pollution, 4% has a low vulnerability and 5% of the wellfield area has a very low vulnerability. The above percentage areas portraying the above levels of vulnerability were investigated in terms of the DRASTIC coefficients. Drastic coefficients vary in the range of 110 to 190. The results of this study indicate that the Kanye wellfield may be highly vulnerable to pollution if not properly managed. However, one should be cautious in the interpretation of these results due to the sparse and uncertain nature of the basic data used for this interpretation, and the inherent variability of the aquifer parameters. The use of the polynomial estimator enabled consideration of simple uncertainty for the aquifer media characteristics modelling process, uncertainty being proportional to the size of the polygons. Estimates of the aquifer media characteristics in areas with only a few observations or few geological logs were considered to have higher uncertainty than areas with many observations. In general, there is a high uncertainty of the groundwater pollution vulnerability classes in the Kanye aquifer system. The Northwest and Rammonedi wellfields have high uncertainty in the classes, while Kgwakgwe wellfield portrays a low level of uncertainty. From the aquifer protection and management point of view, the question is how far one should establish a protection zone around the wellfield so as to protect the entire aquifer from pollution. This needs more study and field checking of the aquifer media characteristics maps. The results presented here are preliminary findings on the use of spatially distributed point data to assess the regional variation of aquifer media characteristics and vulnerability to groundwater pollution.


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The present study shows how vulnerable the Kanye wellfield is to pollution. It therefore underscores the need enforcement of the recommendations by the Department of Water Affairs (1993) to establish groundwater protection zones over the most vulnerable aquifer. REFERENCES Aller, L.T., Bennett, J.H. and Hackett, G., 1987.“DRASTIC: a standardized system for Evaluating Groundwater pollution Potential using Hydrogeoloic setting”. US Environmental Protection Agency Report EPA/600/2–87/035, 622 pp. Beekman, H.E., Gieske, A. and Selaolo, E.T., 1996. GRES: Groundwater Recharge Studies in Botswana, 1987–1996. Botswana Journal of Earth Sciences 1:1–17. Bekesi, G. and McConchie, J., 2002. The use of aquifer media characteristics to model vulnerability to contamination, Manawatu Region, New Zealand. Hydrogeology Journal, 10:322–331. DWA, Department of Water Affairs, 1993. Protection Zones and Guidelines for Major Wellfield, Aquifers and Dams in Botswana. Report prepared by Water Surveys, Botswana. Alemaw, B.F., Shemang, E.M. and Chaoka, T.R., 2004. Assessment of Groundwater Pollution Vulnerability of the Kanye Wellfield, Southeastern Botswana—A GIS Approach, B. Journal of Physics and Chemistry of the Earth, Elsevier Science Publishers (accepted for publication).

The effect of socio-economic activities on watershed management: the case study of Gaborone Dam catchment in Botswana George S.Thabeng & Daniel B.Kemiso Department of Water Affairs, Gaborone Water Resources of Arid Areas—Stephenson, Shemang & Chaoka (eds), © 2004 Taylor & Francis Group, London, ISBN 04 1535 913 9

ABSTRACT: Watershed management entails integrated resource use planning, conservation as well as institutions and organizations involved therein. Issues like environmental concerns, livestock production, fishery, piggery, chicken farming or mineral processing, social and cultural concerns, infrastructure planning as well as involvement of all stakeholders in decision making during planning and implementation stages are of great importance. The most important factors in the whole planning process and implementation of activities in the logistic integrated resources management in which community (owners) involvement and accountability of implementers at all stages from formulation to programmes to evaluation and monitoring are of great importance. This case study looks at one of the socio-economically important river basins in Botswana namely; Gaborone Dam catchment to illustrate watershed management approach. The Gaborone catchment area is very important to our City in terms of agriculture, fishing, poultry, piggery, flour milling, Wildlife management and habitat for important flora and fauna. It covers parts of four administrative regions namely; Kweneng, Ngwaketse, Lobatse and Balete Districts. Since the resource in this catchment transcend administrative and sectoral planning borders of one region, resource use conflicts have emerged over years in the use of land, water and other natural resources. This case study looks at the socio-economic activities in the Gaborone catchment and the emerging trends and conflicts as well as environmental degradation as a result of sectoral planning. Finally the case study analyses the efforts of the Government, interested parties and stakeholders to implement integrated natural resources management by involving local communities in the catchment as well as resolving emerging resources use conflicts.


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1 INTRODUCTION Gaborone Dam was first built in 1963 to supply water to the urban centre of Gaborone when demand for water by the town exceeded the supply from the older Notwane Dam and from boreholes that had been drilled in wellfields in the vicinity of the City. As the City of Gaborone continued to grow and, with it, the demand for water by the City, the Gaborone Dam wall was raised by 8 metres to its present height in 1986. The main technical characteristics of the Dam are as follows: Catchment Area: CapaCity of Dam at f.s.l: Type of Embankment: Crest Length: Maximum Surface Area: Maximum Depth: Average Depth of Water at f.s.l: Potential Evaporation:

14,300km2 141.4×106m3 Rock Earthfill 3km 1900ha (19km2) 20 metres 7 metres

2000mm per year

The catchment area covers the southern portion of southeastern Botswana, and also falls within the neighbouring country of South Africa (Figure 1). It falls within 3 different districts and apart

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Figure 1. Location of Gaborone Dam catchment area. from the southern part of Gaborone City, covers two main primary settlements (urban areas), ie Lobatse in the south and Kanye in the west. The 3 districts are South East District covering approximately 45% of the study area, Southern District covering approximately 47% of the District, and Kweneng which accounts for about 1%, whilst the remaining 7% falls within South Africa. The study area (falling within Botswana) measures approximately 14,300km2 in extent. The southern and western parts of Gaborone are considered as falling within the catchment, and it is the activities in the Gaborone area, that is a major driving factor in the land use problems encountered in the catchment area. 2 THE PHYSICAL ENVIRONMENT 2.1 Physiography and landform The area is generally undulating with slopes tending generally SW-NE. A few Hills— notably Kgale Hill and the Polokwe Hill dominate the remnant of the African erosion surface. The Notwane River and its tributaries dominate the drainage of the area.


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2.2 Climate The climate is generally hot with a slight drop in the temperature during the winter months of May to August. Mean temperatures range from 12°C (July) to 28°C (January). Considerable local variations occur so that the winter temperatures in Lobatse are lower than in Kanye or Mogobane. Winter frost is common in places like Lobatse, Kanye and surrounding areas. Annual average rainfall (1925 to 1997) is 509.6mm in Kanye, and 555mm in Lobatse. Maximum annual totals recorded in Kanye and Lobatse are 970.6mm and 1070.4mm compared to minimum rainfalls of 104.7 and 262.1 respectively. 2.3 Geology and Geomorphology 2.3.1 Geology The geology of the area is complex. The catchment overlies part of the Kaapvaal Craton, an ancient stable segment of acidic crustal rocks. These are Archaean metamorphics, profoundly altered by heat and pressure, as well as igneous rocks. These form the floor above which Proterozoic and younger non-metamorphic sedimentary and volcanic rocks occur. Of the supercrustal rocks, the Lobatse Volcanic Group is the oldest. They now form the arc of rugged relief that extends south of Gopane to Lobaste and northwards towards Mogobane before striking northeast to the north of Ramotswa station. The next, younger rocks belong to the Transvaal Supergroup, one of the major early Proterozoic sedimentary successions, some 5000m thick. The youngest of the supercrustal rock sequences is the Waterberg SuperGroup, the orthoquartite member (Mannyelanong Formation, 17,000–22,000 million years) being responsible for the flat cappings on the interfluves of the project area. Much of the catchment, including the Gaborone Dam, is underlain by the Gaborone Granite (1600–4000m.y). There are also other intrusive rocks in the area, which may be unrelated to the Gaborone granite. These are the Kgoro Complex and Mmathethe Granite (1600– 4000m.y), also dolerite sills and sheets (e.g intruding the granite at Kgale Hill) of late Proterozoic age. Younger Palaezoic and Mesozoic rocks are completely absent from this area. Minor calcretes occur in the soils above the volcanics of the Transvaal Supergroup and minor pedogenic laterites occur in flat locations over the granites. The tectonic history of these ancient rocks is complex and many of the streams of the catchment are strongly controlled by the structures. Unlike in other areas of Transvaal Supergroup rocks, the economic geology of this area has proved very disappointing, despite substantial exploration. The only metal, which has been mined in area, is manganese at Ramotswa, Otse and Kgwakgwa at Kanye. Occurrences are, however limited in the area and thickness. All mining has now ceased, that at Ramotswa in 1958 and at Otse in 1996. There are no foreseeable prospects of pollution of the Gaborone Dam water by run off from metalworking. As concerns


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industrial rocks and minerals, clays, river sands and gravels have been and still are worked for brick making and aggregate. 2.4 Geomorphology 2.4.1 Weathering The catchment comprises surfaces, plains and bottomlands, of predominantly PostAfrican Surface age. The African erosion Surface was the first to form when Gondwanaland split up into the continents of Africa, South America, India, Australia and Antarctica. It is known to have been deeply weathered and weathering was advanced in the sense that primary minerals were converted first to 2:1 clays and in the upper parts of the profile where weathering was more aggressive the 2:1 clays were converted to 1:1 clays, predominantly kaolinite. This weathering involved severe leaching, so that virtually all of the bases, essential nutrients, were removed. Very small areas of African erosion surface survive on the interfluves as small mesas or plateaux, particularly where Waterberg quartzites form cappings. The deep weathering profiles have been stripped off, leaving an interestingly etched rock surface. A good example is the plateau on which Kanye sits. The plateau is deeply penetrated by fossil gorges, terminating in huge dead waterfalls, which clearly attest to formerly much wetter conditions. The fasts of such plateaux, only penetrated with difficulty, provide sufficient isolation for the survival of kudu and leopard. The sharp drop to the Post-African Surface plains, provides the perimeters of such plateaux with many excellent, but rarely visited, view points offering wide vistas over the inselberg-dotted lowlands. Continental uplift and erosion resulted in the formation of the Post-African Surface, which dominates the project area. Weathering is much less advanced, although deep in places. Clay formation is poor. Typically, weathering has only succeeded in separating the individual mineral components of the rock, leaving them in situ as a disaggregated mass. Such poor weathering yields saprolite (weathered rock) with very little cohesion. It is very susceptible to erosion. The poor development of clays results in poor, thin sandy soils, particularly where the rocks are acidic, e.g. in granitic areas. Here the soils are sandy, dominated by quartz and orthoclase feldspar particles, the most resistant to weathering. The small, isolated Hills, which dot the plains are the exposed parts of the basal surface of weathering (the boundary between weathered and fresh rock). The relative relief on the basal surface of weathering is high in granitic areas; the boundary plunges up and down very abruptly, controlled by the frequency of fracturing. Small outcrops form koppies, larger outcrops inselbergs. These shed rainwater so that weathering is facilitated around their bases. 2.5 Soils Soils in the catchment area are generally of the sandy loams, clays and sandy clay loam types. Good fertile soils are found at depositional areas such flood plains and depressions. In the Gaborone area, soils on alluvial deposits are developed in Notwane and


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Segoditshane flood plains where ephemeral rivers bring sand from upstream. These soils are suitable for trees. 2.6 Hydrology and water resources The area is drained by quite a number of ephemeral streams. At the western part of the catchment area are river tributaries such as Gamoralo, Matlhapise, Mokape, and Masinyetse. To the southern part are Gamoswana, Molapowabojang, and Lobatse (from South Africa). The central catchment area consists of Makwena, Molopye, Chawe, and Potsane Rivers. The northern part is the Kgamagadi River. The main rivers in the area that contributes to the Dam reservoir are the Notwane, Nywane, Maratadibe, Fikeng, Metsemotlhaba, Taung, Nywane and Peleng. The hydrological characteristics of the rivers are said to be changing. The river system has become depositional rather than being erosive thereby causing floods. This is noticeable particularly of the Metsemotlhaba, Notwane and Taung rivers, which are prone to flash flooding during rainy season thereby causing Damage to properties and severing of communication linkages between Ramotswa and Tlokweng and the rest of the country. 2.6.1 Wetlands There is a large wetland in the valley of the Taung river, near the village of Mogobane. This wetland is at least 750ha in extent and it currently supports dense wetland vegetation including fragmitis. As will be discussed later, this wetland presents an opportunity for pollution control for Gaborone Dam. All water from the western part of the catchment, i.e. the areas of Khanye, Ranaka, Magolhwane, Ntlhantlhe, and Lotlhakane; will pass through this wetland before entering Gaborone Dam. If properly maintained, the Mogobane wetland will filter and improve the chemical quality all the water from the Taung river and its tributaries before it enters Gaborone Dam. 2.6.2 Aquifers/wellfields The main aquifers in southeastern Botswana are well represented in the project area in the form of two major aquifers, both of which have been targets for exploration. These are the dolomitic aquifers in Ramotswa-Lobatse and Kanye. 2.7 Ecology 2.7.1 Vegetation The Gaborone Dam catchment area comprises a diverse array of vegetation types. Extensive areas of the catchment comprise typically flat sandveld savanna which has been heavily cultivated and is covered by a high proportion of cleared fields, actively growing crops and abandoned fields. The dominant vegetation types in this area are


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acacia dominated bush savannas and tree savannas which range in density from low density areas close to settlements to high density areas in less settled and cultivated areas. Rocky Hills and kopjes occur throughout the catchment area and are generally covered by medium density woodland and bush which shows a high degree of variation in species composition depending on local soil conditions. The rocky outcrops and surrounding Hilly areas are not cultivated and have few settlements, although the runoff from their slopes, following intense rainstorms, contributes significantly to soil erosion on the heavily grazed and cultivated lowlands. Apart from the rocky Hillslopes, considerable concern also surrounds the integrity of the riparian fringes, which experience heavy grazing by domestic stock. Vegetation along the river channels such as Notwane in Gaborone and Peleng in Lobatse exhibit a different shrub and tree cover, which is different from the accustomed savanna type. In view of its uniqueness, the Department of Museum and National Archives has planned to preserve a 2km length and 100m-wide corridor along the Notwane River. 2.7.2 Fauna (Wildlife) Wildlife in the catchment area is low when compared with the northern part of the country. Despite this, quite a number is found in the area. Some little wildlife is found at the Kgale Hill in Gaborone, 300 bird species and a vulture colony called Manyelanong near Otse Hills are also in existence. The area also contains 2 private owned natural reserves; St. Clairs Lion Park and Mokolodi Nature Reserve. The Gaborone Dam and the Sebele sewage ponds are home to over 40 species of water birds. The Gaborone Game Reserve has a large number of antelopes, warthogs ostriches and rhinos. 2.7.3 Crocodiles The occurrence of crocodiles in the Gaborone and Notwane Dams also deserves explicit attention. The Nile Crocodile has in general shown a drastic and well documented decline worldwide, and while not yet endangered, has slipped to a “vulnerable status” (IUCN, 1982). Botswana’s population is concentrated in the Delta, with considerable debate surrounding the size of the pre commercial harvesting (i.e. pre- 1957) crocodile population in the Delta, with estimates varying from a population of 21,000 up to 66,000. 2.7.4 Fisheries Although the fisheries potential of the majority of Dams in eastern Botswana is largely unexploited, Gaborone Dam makes a significant contribution to both the diet and livelihoods of people. Barbus sp. tend to be an abundant and unexploited resource in most Dams throughout the country, probably because such time consuming activities as cleaning and post-harvest processing are essential if the fish is not to be spoilt (Nermark and Mmopelwa, 1994). Good-sized bream appear to be in demand from the larger towns, although local people often prefer catfish (C. gariepinus), a species which is not only drought resistant, but can greatly increase the fish biomass of reservoirs (Nermark and Mmopelwa, 1994).


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3 THE PROBLEM The City of Gaborone has been expanding at a phenomenal rate throughout the past decade and it is still continuing to grow. In a period of 30 years, the population of Gaborone has grown by more than 10 times (Table 1). This growth is the single most important factor underlying the phenomenal growth of population in the catchment area as a whole. The population of the catchment area has been growing over the years. In 1971, the catchment area’s population was 133, 211; by 1981 it had increased to 237, 247 at a rate of 5.8 per cent. The 1991 population census indicates that the area’s

Table 1. Population statistics for Gaborone. 1971a 1981a Growth 1991b rate (1971– 1981)

Growth 2001c rate 1981– 1991)

17,718 59,657 12.1% 133,468 8.1%

Growth rate (1991– 2001)

186,007 3.3%

population increased further to 338,068 at a rate of 3.5 per cent. The recent population census held in 2001 indicates a growth of about 3.1 percent in the catchment area. The present population is therefore estimated at 458,370 (see Table 1). The growing urban areas such as Gaborone, Lobatse, Ramotswa, and Kanye, have been the main nuclei for the population pull and hence their growth. These centers have now become dormitory towns for Gaborone, with substantial numbers of people commuting from them to work in Gaborone daily. The highest growth rates between 1991 and 2001 are recorded for Otse, Gaborone, and Gabane ranging between 3.3 per cent and 5.5 per cent. This is as a result of some pull factors (migration) such as economic opportunities, social, educational and recreational activities, which have attracted people to these centres. The growth described above is driving a scramble for land in the catchment area. This in turn has resulted in land use and land development problems. The problem is exacerbated by the fact that land administration within the catchment area falls under the jurisdiction of many authorities, with very little coordination. As a result, the catchment area is experiencing water quality problems. A case in point is in Ramotswa, in the South East District, where although it has abundant ground water, it has been polluted by human waste. More importantly, the water in Gaborone Dam on which the City depends is also affected. The present situation regarding the chemical aspects of the water quality is that it is excellent, falling well within BOBS standards for Class 1 water (Ideal), although aesthetic parameters (odour and taste) have, on occasions been unacceptable. There is a long term trend towards increase in solutes, conductivity and pH, superimposed on seasonal patterns. The cause appears to be regional rather than local, but further research into this is needed. Of some concern is the tentative conclusion that normal rains do not result in very substantial washing of surface materials down into the Dam. These appear to accumulate until above average rainfall conditions are experienced. In effect the catchment stores surface materials, possibly for many years before they are delivered to the Dam. This enhances the already pronounced seasonal patterns of delivery. Data on


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the biochemisty and biology of the Dam water are, at this point, inadequately monitored and it is largely this aspect of water quality which could be of concern (Aqualogic, 2002) 4 THE CAUSES OF THE PROBLEM The causes of the problem should be discernible from the foregoing. Without doubt, the problem is the direct consequence of development in the catchment area without adequate controls. This is the sort of problem that watershed management approach to resource development and utilization could have helped to avoid. In the case of the Gaborone Dam catchment area, the problem can be attributed to the land use and land administration problems. Land ownership in the country is either freehold or tribal (customary law). A large percentage of the study area falls under tribal land, (ie, more than 70%) and is administered under the jurisdiction of several Land Boards (Balete, Bakwena, Ngwaketse, Malete). Usage rights can either be granted communally or to individuals. The majority of residential and agricultural sites are therefore held under customary law land rights, while those for commercial, industrial and institutional are held under common law (leasehold). Customary grants are not registered at the Deeds registry but only at the Land Board. It thus cannot be used as collateral security for the raising of mortgage finance unless surveyed and converted into common law. Freehold land on the other hand, permits management of the land to rest with the owners in accordance with legislation such as the “Agricultural Resources Conservation Act” (Cap 35:06). This legislation puts restrictions on the owner in terms of actual tenure, sales and leases. The study area reflects a range of allocation patterns in various stages of transformation from a traditional pattern to the more recent contemporary (modern) layouts. The study area falls within two countries—Botswana (93%) and South Africa (7%). The land uses in Botswana’s Section can be defined in two broad categories. The first category relates to those predominantly rural uses situated outside the built-up areas of the villages and towns, whilst the second are those uses of an urban nature situated within the boundaries of the villages. The catchment/study area is made up of the built-up areas (settlements), areas of agriculture (both cultivation/cropping and grazing), waterbodies/Dams as well as other tourism-related areas and key public facilities. Agriculture is the second largest sector of Botswana’s economy and is the backbone of the rural economy, which supports two-thirds of the national population. Spatially the cropping and grazing (agriculture) component together, makes up the largest land use within the catchment/study area, with grazing making up the majority of the agricultural land, eg Rankoromane Farm near Otse. The second largest land use is the built-up area—which is all the major villages and towns, as well as all the smaller villages like Ranaka and Ntlhantlhe. The waterbodies/Dams land use category, occupy temporarily or permanently some parts of the study area. A very serious problem is caused by the occasional flooding of


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the settlements within the study area. Most of the flooded areas are located in settlements eg Ramotswa. In addition to the above land uses, is the game/nature reserve/parks component, most of which are privately-owned, and related to tourism (eg Mmokolodi, St Clairs Lion Park, Manyelanong Game Reserve, etc). This land use is concentrated to the north and east of the study area, and is one of the smallest land uses within the catchment area. All land within and around the Dam (Forest Hill 9-KO) itself is freehold land. The land use within this area can be categorised into the following uses: industrial, quarrying, residential, commercial, recreational, social and public uses, agricultural and infrastructure, and fall into an area defined as a “greenbelt” and form part of a Regional Park EHES (2002). This portion of the catchment area falls within the jurisdiction of Lehurutshe Council, of the Central District Municipality of the North West Province of South Africa. The land use in this area is a mix of rural/tribal settlements, characterised by low density, scattered homesteads, and privately-owned game farms and/or nature reserves. (A portion of the Madikwe Game Reserve falls within this catchment area.) There are no major public or civic institutions in this portion of the study area, and visually looks like the central and south of the catchment area falling within Botswana. Added to the above is the industrial development taking place in the catchment area. The major economic activity in the catchment area is services, which employs on the average about 45% of the labour force. This is followed by industry, which accounts for about 35% of the labour force with construction employing most people in the industry. Agriculture accounts for about 9% in the catchment area, but however employs more people in the rural areas. Commerce, which entails wholesaling and retailing employs about 11%. Economic activities are concentrated in the Ramotswa area. Over two-thirds of the economic activities (68.1%) are located in and around Ramotswa, and reflects Ramotswa’s proximity to Gaborone; Ramotswa has developed a nucleus of activities in the sectors of grain milling, clothing and furniture industries along with “common” activities such as brick moulding and metal works; ● The most common economic activities are brick moulding, metal works, clothing and furniture production. ● Six tanneries are located in Ramotswa and Kanye. ● Nine scrap yards exist evenly spread over the project area. Livestock production, especially range cattle and goat production, is the main form of agricultural activity in the Gaborone Dam catchment. 4.1.1 Crop production It is observed that the gross maize, sorghum, and beans (pulses) production in the districts is very low. For example, in the 1996/1997 cropping season, which was the best in the records, the whole of Ngwaketse South district produced only 734 tons of sorghum and 916 tons of maize. On the other hand, the same district only produced 15 and 76 tons of sorghum and maize respectively in the 1999/2000 season. These data confirm the point that the catchment is located in an area of very low rainfed crop production potential.


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4.1.2 Range livestock production It is estimated that there are about 125,000 cattle in the catchment, after allowing for the fact that the catchment only takes 10% of Ngwaketse South extension district. The goat population in 1996 was in excess of 175,000. 4.1.3 Dairying There are dairy operations in some of the commercial farms in the eastern part of the catchment area. In the rural sector of the catchment, there are two herds, one at Magobane and the other at Kanye. The former dairy herd had 160 cows in 2001, 77 of them in milk and producing 1463 litres per day. The Kanye dairy comprised 103 cows in 2001, 50 of them in milk and producing 640 litres of milk per day. From an environmental point of view, dairy operations can be a source of water pollution when animal wastes wash into public streams and lakes. The Magobane dairy is the largest dairy close to Gaborone Dam and it is situated on the banks of the Taung River. Fortunately, however, the dairy is adjacent to and upstream of the Magobane wetland. Thus, any wastes that are released from the dairy into the Taung River are likely to be trapped by the wetland, and are therefore unlikely to have a significant direct pollution impact on Gaborone Dam. 4.1.4 Poultry Lately there has been an upsurge in small-scale commercial poultry production in all the villages. Small groups of farmers in most of the villages of the catchment have constructed chicken houses that accommodate between 500 and 6000 chickens at any one time. Chicken manure is rich in nitrogen and therefore has a high potential for polluting water bodies if directly released therein. It was further observed that the manure or waste from these chicken operations is not carefully stored or disposed of. There is a risk of some of this manure being washed directly into the Notwane River and into the Dam. Thus in summary, the problem of pollution in the Gaborone catchment area may be attributed to: ● Land administration problems: different authorities administering land in the same catchment. ● Lack of coordination among the various authorities. ● Land use under different sovereignties—RSA and Botswana. ● Industrial development within the catchment area.

5 ACTION In order to address the problem, a number of actions have been initiated within the paradigm of watershed management. These actions are: (i) Revision and coordination of land use plans. This study is currently underway.


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(ii) Some industries have embarked upon pre-treatment of wastewater. (iii) Better monitoring schemes have been designed and are being executed by the DWA Pollution Control Unit. (iv) Most urbanized villages in the catchment area are being provided with waterborne sanitation facilities.

6 CONCLUSION Clearly, environmental protection of the Gaborone Dam goes far beyond the protection of the immediate environment. Whole catchment management is increasingly recognized as essential to the protection of any one component within the system. To achieve this, the functioning of the system must be clearly understood. This can be best done by adopting the paradigm of watershed management. REFERENCES DWA (2002), Environmental impact assessment consultancy for the feasibility study of small to medium Dams in eastern Botswana, Aqualogic Pty Ltd. Final report. Department of Town and Regional Planning (1995). Gaborone Landscape Masterplan 100 pp. EHES (PTY) LTD (2002). A strategic environmental assessment for the Gaborone Dam catchment area. IUCN (1982) Amphibia-Reptilia Red Data Book. Part I. Testudines, Crocodilia, Rhinchocephalia. 426 pp. Nermark, U.P. and Mmopelwa, T.G. (1994). Utilization of small water bodies, Botswana: report of activities towards fisheries exploitation, 1992–1993. Harare (Zimbabwe). 36 pp.

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Author index Ahmed, A.M. 547 Alemaw, B.F. 551, 559 Andam, K.A. 175 Anyemedu, F.O.K. 169 Aslan, Ş. 477 Asmellash, M. 59 Awuor, V.O. 35 Balachandran, K.K. 67 Bauer, P. 03 Bean, J. 73 Bennie, A.T.P. 397 Böttcher, J. 379 Brunner, P. 03 Carter, R.C. 467 Chaoka, T.R. 551, 559 Chavarro, D.C 239, 341, 541 Chengeta, Z. 451 Clarke, S. 143 Cobbing, A.J.E. 87 Davies, J. 87 Dennis, I. 73, 79, 115, 429 Dennis, S.R. 297 Diiwu, J.Y. 347 Drury, S.A. 59 du Preez, M. 297 Duijnisveld, W.H.M. 379 Ellington, R.G. 47 Engelbrecht, P. 143 Farah, H.O. 331 Farr, J.L. 315 Folwell, S.S. 507 Fregoso, A. 541 Frengstad, B. 97 Fry, M.J. 507 Gumiremhete, R. 315

Author index

Hassan, M. 467 Himmelsbach, T. 379 Hötzl, H. 379 Hodgson, F.D.I. 363 Houghton-Carr, H.A. 507 Hussin, Y.A. 239, 341 Ibrahim, A.E. 247, 259 Idowu, E.O. 227 Ilemobade, A.A. 419 Iliya, A. 279 Ilunga, A.M. 23 Keeletsang, M. 541 Kellner, T. 315 Kemiso, D.B. 565 Kheiralla, K.M. 247, 259 Kinzelbach, W. 03 Kistamah, N. 529 Kooke, S.O. 35 Kumar, A. 59 Kumar, H. 323 Lubczynski, M. 239 Lubczynski, M.W. 97, 271, 285, 341, 541 Machingambi, M. 181 Machiridza, R. 181 Mafa, B. 133 Magombedze, L.M. 97 Magowe, M. 29 Makobo, P. 29 Makuya, M. 519 Manzungu, E. 181 Mapanda, W. 541 McCartney, M. 493 Mishra, G.C. 105 Mkwizu, Y.B. 157 Molwalefhe, L. 459 Molwalefhe, L.N. 409 Mpala, T. 201 Msangi, J.P. 207 Mudzingwa, B. 315 Mugabe, F.T. 501 Mulwa, J.K. 303 Muyima, N.Y.O. 535 Mvungi, A. 519 Ndiritu, J.G. 445

738

Author index

Nkotagu, H.H. 157 Ntsatsi, J. 323 Nyarko, K.B. 169, 217 Nzaba, A.S. 331 Obakeng, O. 239, 271, 285, 341, 541 Obakeng, T. 29 Odai, S.N. 169, 175 Oduro-Kwarteng, S. 169 Olubode-Awosola, O.O. 227 Omoto, W.O. 35 Opere, A. 357 Opere, A.O. 35 Paimpillil, J.S. 67 Pironcheva, G. 535 Pretorius, J. 79 Rooke, E.R. 485 Roseunee, S. 529 Rushton, K.R. 467 Sally, H. 493 Sbeih, M.Y. 191 Scheuerlein, H. 435 Schwiede, M. 379 Selemani, M. 515 Senzanje, A. 493, 501 Sharma, T.C. 331 Shemang, E.M. 279, 323, 551, 559 Siegfried, T. 03 Sitters, C.W.M. 331 Stadler, S. 379 Staudt, M. 371 Stephenson, D. 23, 419, 451 Tesfaslasie, F. 59 Thabeng, G.S. 565 Totolo, O. 551 Tredoux, G. 143 Trifunovic, N. 175 Türkman, A. 477 Uka, Z.B. 507 Umoh, U.T. 389 Usher, B. 79 Usher, B.H. 47, 123, 363 van Tonder, G. 73, 429

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Author index

van Tonder, G.J. 17, 47, 115, 297 Veltman, S. 123 Vermeulen, D. 429 Vermeulen, P.D. 17 Viswanatham, K.S. 59 Vogel, H. 133, 371 von Hoyer, M. 379 Vriend, S. 459 Woyessa, Y.E. 397 Yilmaz, L. 151 Zamxaka, M. 535 Ziwa, C. 541

740

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