REPUBLIC OF BOTSWANA Ministry of Mineral, Energy and Water Affairs DEPARTMENT OF WATER AFFAIRS Maun Groundwater Development Project Phase 1: Exploration and Resource Assessment Contract TB 1013126194·95 FINAL REPORT October 1997 Eastend Investments (Pty) Ltd. JOINT VENTURE OF: Water Resources Consultants (Pty) Ltd., Botswana and Vincent Uhf Associates Inc., USA Ministry of Mineral, Energy and Water Affairs DEPARTMENT OF WATER AFFAIRS Maun Groundwater Development Project Phase 1: Exploration and Resource Assessment Contract T8 1013126194-95 FINAL REPORT Executive Summary October 1997 Eastend Investments (Pty) Ltd. JOINT VENTURE OF: Water Resources Consultants (Ply) Ltd.• Botswana and Vincent Uhl Associates Inc., USA MAUN GIIOUNOW"TEA DEVELOfOMEHT PAOJECT PHolSE I FI""llIepan. CONTENTS 1.0 INTRODUCTION 1 1.1 Background 1 1.2 Project Goals and Objectives 1 1.3 Reporting 2 1.4 Project Location and Setting 3 2.0 OVERVIEW OF MAUN WATER SUPPLy 3 3.0 INVESTIGATION PROGRAMME 4 3.1 Inception Period 4 3.2 Field Exploration Programme 5 4.0 DISCUSSION OF RESULTS AND FINDINGS 6 4.1 Shashe Wellfield 7 4.2 Exploration Areas Summary 7 4.3 Groundwater Quality 8 4.4 Natural and Artificial Recharge 9 4.5 Other Findings 9 5.0 RECOMMENDED DEVELOPMENT PLAN 11 5.1 Introduction 11 5.2 Stage 1: Immediate implementation (1998) 12 5.3 Stage 2: Medium Term (2000 - 2012) 13 5.4 Stage 3: Longer Term Development 15 6.0 CAPITAL COSTS 15 7.0 CONCLUSiON 16 8.0 REFERENCES 17 9.0 ACKNOWLEDGEMENTS 27 MAUN GROUNDWATER DEVELOPMENT PROJECT PHASE I FI....I Rtpo<t TABLES E-1. Summary of Exploration Work Completed E-2. Comparative Analysis of Exploration Areas E-3. Statistics on Exploration Borehole Data E-4. Comparative Costs for Development Scenarios - Stage1 E-5. Comparative Costs for Selected Development Scenarios - Stages 2 & 3 E-6. Comparative Costs for Artificial Recharge Schemes FIGURES E-1. Project Area Location Map E-2. Location of Exploration Areas E-3. Annual Surface Water Flow of the Okavango River at Mohembo and Selected Distributaries E-4. Percentage of Recorded Water from Each Source (1989 to 1996) - Maun Water Supply E-5. Digital Terrain Map E-6. Landsat Thematic Mapper Image E-7. Airborne EM Conductance Map E-8. Comparison of Exploration Area Boundaries at Inception Period and Final Exploration Areas E-9. Artificial Recharge Test Site in Shashe River Valley E-10. Borehole Location Map for Shashe RiverValtey E-11. Geological Cross Section Along the Shashe Valley E-12. Resistivity Section in Upper Boro Valley from TEM Sounding Interpretation E-13. Stage 1, Recommended Development: Shashe and Lower Thamalakane River Valleys E-14. Stage 2, Recommended Development Plan: Upper Thamalakane and Upper Boro River Valleys E-15. Project Implementation Schedule E-16. Outline of the Resource Development Plan for Maun t£sl.~d 10'-"1""." ('1)') L'd: Jol.' V'.I~...rW'I'" R<No,_ C.....ll.... ('Iy) Ltd.. Bo".·••• oad VIa...1Ukl AJoo<I.... I.... USA ii MAUN GROUNDWATER DEVELOPMENT PROJECT PHASE I EXECUTIVE SUMMARY 1.0 INTRODUCTION 1.1 Background The Maun Groundwater Development Project (MGDP) was initiated by the Department of Water Affairs (DWA) following the Botswana Government's decision to terminate the Southern Okavango Integrated Water Development Project (SOIWDP) in May 1992. SOIWDP was a large engineering study that proposed the utilisation of surface water to meet a number of water demands, including Maun's, on the southern fringe of the Okavango Delta. The MGDP consisted of five separate and related contracts which included: an Aeromagnetic SUivey (World Geoscience Botswana), an Airborne Electromagnetic Survey (World Geoscience Botswana), Groundwater Exploration and Resource Assessment (Eastend Investments). Drillin9 (R. A. Longstaff and DeWet Drilling) and an Environmental Impact Assessment (Geoflux). The Groundwater Exploration and Resource Assessment contract was awarded to Eastend Investments (pty) Ltd. [a joint venture of Water Resources Consultants (Pty) Ltd., Botswana and Vincent Uhl Associates, Inc., USA} and the contract between DWA and Eastend was signed on 17 August, 1995. The Project Area is located in the northwestern part of Botswana in Ngamiland District (Figure E~1). It covers an area of 12,500 square kilometres and extends from the Khwai River (Mababe Village) in the northeast to Lake Ngami (Toteng Village) in the southwest (Figure E~2). Part of the Project Area lies at the distal end of the Okavango Delta and the major delta distributaries flow through the Project Area (Figure E~2). The Okavango Delta has been designated as a Wetland of International Importance as per The Ramsar Convention to which the Government of Botswana is a signatory. The climate in and around the Project Area is semi-arid to arid. Average annual rainfall ranges from 546 mm (1945-1996) at Shakawe to 455 mm (1922-1996) at Maun. Annual potential evapotranspiration at Maun usually exceeds 2,000 mm. The area is characterised by extremely low topographic relief. The geology of the area consists of thick sediments of the Kalahari Beds which are underlain by bedrock units inclUding the Karoo Supergroup of Carboniferous to Jurassic Age and the Damara Supergroup of Paleozoic to Proterozoic Age. The region lies within an area of continued earthquake activity and is located on the southern end of the seismically active African rift system. 1.2 Project Goals and Objectives The primary goal of the Project was to assess groundwater availability and development potential within the Project Area to meet the present and projected year 2012 demand for Maun. The latter was estimated to be 4 million cubic metres (MCM) per year by the Botswana National Water Master Plan (BNWMP. 1991). MAUN GROUNDWATER DEVELOPMENT PROJECT PHASE I FINI R""on A secondary goal was to assess the feasibility of implementing the groundwater related recommendations contained in the International Union for the Conservation of Nature and Nalural Resources (IUCN) 1992 Report. The principal Project objectives were to: • Locate potential areas for groundwater exploration and assess development potential in these areas. • Assess, in these potential areas, aquifer hydraulic characteristics, groundwater flow conditions, aquifer geometry, volumes of fresh groundwater in storage, natural recharge characteristics, and extractable resources for water·supply development. • Assess the costs of resource development and provide preliminary design concepts for new production wellfields. • Establish monitoring systems (seismic, rainfall and water level). • Evaluate water losses in the existing reticulation system and recommend remedial action. • Assess the feasibility of artificial recharge in the Shashe River Valley as a means of extending the life of this wellfield. • Provide a recommended development plan to meet immediate, medium (year 2012) and longer term (year 2027) water supply needs for Maun. 1.3 Reporting The results of the groundwater exploration and resource assessment programme are presented in various reports. The Executive Summary summarises Project activities, principal findings and recommendations; and the Main Report provides an in depth summary. Associated with the Executive Summary and the Main Report are 15 additional reports or appendices each describing a specific technical aspect of the Project. APPENDIX TITLE Appendix A Vegetation Analysis Appendix 8 Geomorphology and Sedimentology Appendix C Geology and Structure Appendix 0 Hydrological Analysis Appendix E Artificial Recharge Study Appendix F Water Audit and Leak Detection Study Appendix G Shashe Wellfield Management Report Appendix H-Vol. 1 Modelin9 of Shashe Wellfield Appendix H-Vol. 2 Modeling of Exploration Areas A to D Appendix I-Vol. 1 Airborne and Ground Geophysics Appendix I-Vol. 2 Geophysics Data Books Appendix J Project Data Books Appendix K Hydrochemistry and Environmental Isotopes Appendix L Recharge Assessment Appendix M Micro Seismic Study £.".nd 1"""''''''''(''1') LId: J"I,,' v... ,~,. "rw.,... ~.'"" C....ll..... ("~l L'd.• Bou..·.n•••d IIi,,'tnl U~I A....n.I.. In<.. USA 2 MAUN GROUNDWATER DEVELOPMENT PROJECT PHASE I 1.4 Project Location and Setting The Project Area is located at the distal end of the Okavango Delta and groundwater exploration activities were concentrated along outlet valleys of the delta, which during the study period were mostly dry. An analysis of long-term flow records of inflow into the delta at Mohembo and outflow from the delta in the Bora River system indicates that on an average, 2 percent of the inflow is manifested as outflow with the average outflow in the Boro River being about 200 MCM per year. Figure E-3 provides a plot of annual surface water flow of the Okavango River at Mohembo and for selected delta distributaries in the Project Area. The Thamalakane River, a major watercourse in the Project Area receives flow from several Okavango River outlets, the primary being the Boro River at present. Secondary outlets that are also tributary to the Thamalakane River include the Nxotega, Shashe, Boranyana, Santantadibe, and Gomoti Rivers. The annual floodwaters usually enter the Boro River between June and August, peak in July or August and diminish from September until the next annual flood. The secondary outlets receive flow intermittently, only during wetter years. The Nxotega River did not flow this decade. The Shashe River Valley, in which Maun's main wellfield is located, has not seen surface water flow since 1989: this has resulted in a lack of recharge to the Shashe aquifer system and the decline of groundwater availability. The Kunyere River system, in the southwest part of the Project Area, receives delta outflow via the Marophe, Xudum, and Matsibe Channels. The Kunyere River flows from northeast to southwest along the Kunyere Fault and empties into Lake Ngami. This river system, like the secondary outlets that are tributary to the Thamalakane River, only flows during wetter years. The last time that flow was recorded at the gauging station at Toteng was in September 1992. The Mogogelo and Khwai Rivers are northeastern outlets from the delta and drain to the Mababe Depression.