REPUBLIC OF BOTSWANA DEPARTMENT OF GEOLOGICAL SURVEY MATSHENG AREA GROUNDWATER INVESTIGATION (TB 10/2/12/92-93) TECHNICAL REPORT T3: INVENTORY REPORT SEPTEMBER 1994 Prepared by ~.... -~~ .. INTER WELLFIELD .~" CC)NSULT In association with : :I BRITISH GEOLOGICAL SURVEY Keyworth , Nottingham, UK MATSHENG AREA GROUNDWATER INVESl'IGATION Technical Report 1'3: InventoI)' Report September 1994 LIST OF CONTENTS 1. INTRODUCTION. 1 2. BACKGROUND. 2 2.1 Project Objectives ..................................... 2 3 SETTLEMENTS AND LAND USE ............................ 3 3.1 Population. 3 3.2 Land Use and Land Use Planning . 4 3.2.1 Land Use Planning ......... 4 3.2.2 Livestock ...................................... 6 3.2.2 Crop Production . .. 7 3.2.3 Wildlife ....................................... 7 3.3 Water Supply ........................................ 7 4 METEOROLOGY. 9 4.1 Meteorological Stations . 9 4.2 Rainfall . .. 9 4.3 EvapotransplratlOn. 13 4.4 Sunshine Hours . 13 4.5 Wind Speed and Direction. 13 5. REMOTE SENSING. 14 5.1 Objectives. 14 5.2 Methodology. 14 5.3. Results.. 14 6. BOTANICAL SURVEY .................................... 16 6.1 Objectives. 16 6.2 Methodology .................. , . 16 6.3 Identification of Potentially Shallow Groundwater ............ 16 7. RECONNAISSANCE SURVEYS ............................. 19 7.1 Ground Control Point Survey ........................... 19 7.2 Borehole Reconnaissance .............................. 20 7.3 Water Sampling. 23 7.4 Borehole Siting Methods .. 24 7.5 The Project Database ................................. 24 7.5.1 Sources of Data ................................ 25 7.5.2 Field Data .................................... 29 7.5.3 Main Reconnaissance Database. .. 29 7.5.4 Hydrochemistry Database ......................... 29 7.5.5 Vegetation Database. 30 7.5.6 Use of the Database ........... 30 BRfl'ISH GEOLOGICAL SURVEY WELLFlELD CONSULTING SERVICES Keyworth P.O.Box 1502 Nottingham, UK Gaborone, Botswana MATSHENG AREA GROUNDWATER INV1~TIGATION ii Technica! Report T3: Inventory Report September 1994 8 GEOLOGY ........................... " . ....... .. .. 31 8.1. Previous Work ...................................... 31 8.2 Lithology . .. 31 8.2.1 Stratigraphic Sequence ........................... 31 8.2.2 Basement..................................... 33 8.2.3 Pre Karoo Sedimentary Strata . 33 8.2.4 Karoo Supergroup . 33 8.2.5 The Kalahari Sequence . 35 8.3 Structure. 36 9. GEOPHYSICS. 42 9.1 Regional Geophysical Interpretation ...................... 42 9.2 Geophysical Calibration Survey ....... 43 9.2.1 Investigation of Shallow Aquifers. 43 9.2.2 Investigations at of Deeper Aquifers ................. 53 9.2.3 Investigation of a Calcrete Ridge. 54 9.2.4 Recommendations .............................. 54 10 HYDRO GEOLOGY . 57 10.1 Previous Work and Information Sources ................... 57 10.2 Groundwater Occurrance . 57 10.3 Aquifer Distribution and Properties . 58 10.3.1 Basement ..................................... 58 10.3.2 Pre-Karoo . 58 10.3.3 The Dwyka Group .............................. 58 10.3.4 The Ecca Group . 58 10.3.5 Lebung Group ................................. 63 10.3.6 Kalahari Sequence .............................. 64 11 A CONCEPTUAL HYDROGEOLOGICAL MODEL. .. 70 11.1 General............................................ 70 11.2 The Aquifer Units . 70 11.3 Recharge........................................... 73 12. FIELD INVESTIGATION PHASE. 74 12.1 Geophysics and Exploratory Drilling ...................... 74 12.1.1 Karoo Aquifer Units. 74 12.1.2 Kalahari Aquifer . 75 12.2 Drilling and Aquifer Testing Operations ................... 76 REFERENCES... .. .. .. ................. ...... .... .... .. 77 BRITISH GEOLOGICAL SURVEY WELLFIELD CONSULTING SERVICES Keyworth P.O.Box 1502 Nottingham, UK Gaborone, Botswana MATSHENG AREA GROUNDWATER INVESTIGATION 1I1 Technical Report 1'3: Inventory Report September 1994 LIST OF TABLES TABLE 1 Population Statistics for the Matsheng Villages ............... 3 TABLE 2 Estimate of cattle numbers .............................. 6 TABLE 3 Monthly climatological data for the Tshane Meteorological Station (1958-85) . 10 TABLE 4 Sources of Data. 25 TABLE 5 Project Database Structures . 26 TABLE 6 Stratigraphic Units in the Matsheng Area .................. 32 TABLE 7 Frequency Distribution of Conductivity for Karoo and Kalahari water samples ....................................... 61 TABLE 8 A Summary of Aquifer Test Results from Kalahari Boreholes ... 68 BRITISH GEOLOGICAL SURVEY WELLFlELD CONSULTING SERVICES Keyworth P.O.Box 1502 Nottingham, UK Gaborone, Botswana MATSHENG AREA GROUNDWATER I,,-'VESTIGATION iv Technical Report 1'3: Inventory Report September 1994 LIST OF FIGURES Figure 1 Land Use Plan for the Matsheng Area Figure 2 Monthly Climatological for the Tshane Meteorological Station (1958-85) Figure 3 Monthly Total Rainfall (1989-1994) for Tshane, Hukuntsi, Lehututu and Lokgwabe Figure 4 Botanical Survey: Areas Potentially Shallow Groundwater Figure 5 Borehole Reconnaissance Data Form Figure 6 A Cross Section through Deep Stratigraphic Boreholes Figure 7 Locations of Deep Boreholes in the Matsheng Area Figure 8 Thickness of the Karoo Supergroup and Kalahari Sequence Figure 9 Lehututu Pan Traverse: Interpretation of HLEM data Figure 10 Lehututu Pan Traverse: Interpretation of TDEM data Figure 11 Lehututu Pan Traserse: TDEM Pseudo Section from Smooth Inversion Figure 12 Lehututu Pan Traverse: Electrical Sounding at 100E Figure 13 Hukuntsi Calcrete Ridge: Interpretation of HLEM data Figure 14 Cross Section Through Boreholes Penetrating the Kalahari to the South of Lehututu Figure 15 A Conceptual Hydrogeological Model BRITISH GEOLOGICAL SURVEY WELLFIELD CONSULTING SERVICES Kcyworth P.O.Box 1502 Nottingham, UK Gaborone, Botswana MATSHENG AREA GROUNDWATER INVESrIGATION v Technical Report 1'3: Inventory Report September 1994 LIST OF MAPS Map 1 Borehole Locations Map 2 Well Locations Map 3 Groundwater Conductivity Map 4 Groundwater Levels APPENDICES Appendix 1 Ground Control Point Data Appendix 2 Borehole Data Appendix 3 Well Data Appendix 4 Hydrochemistry Data BIUTISH GEOLOGICAL SURVEY WELLFlELD CONSULTING SERVICES Keyworth P.O.Box 1502 Nottingham, UK Gaborone, Botswana MATSHENG AREA GROUNDWATER INVESTIGATION 1 Technica! Report T3: Inventory Report September 1994 1. INTRODUCTION This report marks the culmination of the Inventory Phase of the Matsheng Area Groundwater Investigation Project. The report provides a detailed account of all field reconnaissance activities undertaken to date, as well as an account of all data gathered regarding geological, hydrogeological and hydro chemical aspects of groundwaters in the area. Also included is information regarding land use and meteorology together with results obtained from Regional Geophysics, Remote Sensing and Botanical Studies. The entire range of information is utilised to develop an integrated interpretation of current hydro geological knowledge for the Project area. This in turn provides the basis for the formulation of the initial hydrogeological conceptual model, presented in this report. Recommendations are provided regarding objectives for geophysical surveys and exploratory drilling to be carried out in the Field Investigation Phase of the Project. BRl11SH GEOLOGICAL SURVEY WELLFlELD CONSULTING SERVICES Keyworth P.O.Box 1502 Nottingham, UK Gaborone, Botswana MATSHENG AREA GROUNDWATER INVESTIGATION 2 Technica! Report T3: Inventory Report September 1994 2. BACKGROUND The Matsheng Area includes the villages of Tshane, Lokgwabe, Hukuntsi and Lehututu and the surrounding area and is located in the middle of the southern portion of the Kalahari. These four settlements, originally developed as a consequence of the presence of shallow groundwater associated with the adjacent major pans. They now form the focal point of development in the region and both human and cattle populations have been growing steadily. In recent years development at Hukuntsi, associated with the establishment of a sub office of the Kgalagadi District Council, has been particularly marked. As a result of the excessive concentrations of both people and animals in the vicinity of the villages, both the land carrying capacity and the water supply system are under great strain. In an attempt to alleviate this problem, a number of land use planning exercises undertaken over the past two decades, have proposed the redistribution of cattle (and hence to a degree human) population over a much broader area This has been attempted by the establishment of commercial ranches (under the Tribal Grazing Lands Programme - TGLP) and better defined communal grazing areas. These plans have been partially implemented but their success has been severely hampered by the lack of adequate water supplies. This in turn has resulted in the continued growth of the villages, with a consequent increase in demand on the already limited local water sources. The availability of adequate water is clearly critical to any future development, in the Matsheng area. The Matsheng Area Groundwater Investigation Project was therefore formulated to assess groundwater resources which may be utilised to satisfy this growing village water demand, and at the same time to resolve the future of the proposed, more widespread, cattle grazing in the area. 2.1 Project Objectives The essential objectives of the Project as stated in the Revised Technical Proposal (RTP) (Wellfield Consulting Services, 1994) were to; a) assess the overall groundwater resources of