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Village water supply in Botswana: assessment of recommended yield for production boreholes in a semi-arid environment
Institution:1. Université de N''Djamena, Laboratoire Hydro-Géosciences et Réservoirs, Campus de Farcha, N''Djamena, Chad;2. Université de Corse Pascal Paoli, Département d''Hydrogéologie, Campus Grimaldi, BP52, 20250 Corte, France;3. CNRS, UMR 6134, SPE, BP52, 20250 Corte, France;4. Ministère de l''Hydraulique Urbaine et Rurale, Laboratoire National des Eaux, BP 1769, N''Djamena, Chad;5. Université de Douala, Faculté des Sciences, P.O BOX 24157, Douala, Cameroon;6. Université de Bangui, Laboratoire Hydrosciences Lavoisier, BP 908, Avenue des Martyrs, Bangui, Central African Republic;7. Ministère de l''Eau et de l''Assainissement, Direction de l''Hydrogéologie, Niamey, Niger;8. International Atomic Energy Agency, Isotope Hydrology Section, Vienna International Centre, PO Box 100, 1400 Vienna, Austria
Abstract:More than 90% of the rural villages and settlements throughout Botswana have water supplies based on groundwater. The annual increase in water demand is about 0.3 × 106 m3 and on average around 60 new boreholes are needed annually. In parallel with construction of new production boreholes for rural villages, there is an on-going rehabilitation of existing boreholes which have lost their original yield due to clogging, corrosion, encrustation, etc. The total annual cost of siting, drilling and testing of around 100 new production boreholes for rural villages water supply is estimated at around US$7.5 million (1997 price).Modelling of every groundwater resource for rural village water supply in Botswana is currently not feasible due to a lack of relevant and detailed information. A modelling exercise will assess the resource of the aquifer being studied, but can not give an assessment of the yield of each production borehole. Groundwater supply to rural villages is therefore currently based on the abstraction possible from established production boreholes. Test pumping data from these boreholes are the prime information in such an assessment. However safety factors and the fact that drought periods of longer duration are common in a semi-arid environment must also be considered. A computer program package TESTCURV developed by the Department of Water Affairs is a most useful tool in the assessment of yields for production boreholes for village water supply in Botswana, based on the performance of the well and the aquifer. No replenishment is assumed and the question of sustainable yield is not addressed by the program.
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