An exploration strategy for higher-yield boreholes in the West African crystalline basement

Abstract

Abstract In Burkina Faso investigations have been carried out to test satellite imagery and electromagnetic (EM) methods as a means of improving the siting of water supply boreholes in fissured rocks of the crystalline basement. The results show that these methods may be used to locate boreholes with above average groundwater yields, and to reduce the failure rates. Geometrical analysis of Landsat-MSS lineaments reveals the relevant regional fracture pattern, the present-day principal stress field and the resulting system of oriented hydraulic conductivities. Structural analysis of the lineament pattern and identification of dry-season-active vegetation on Landsat-TM imagery permit promising locations to be pinpointed for groundwater abstraction. EM-measurements on a two-dimensional grid using the ‘very low frequency’ (VLF) and ‘horizontal loop EM’ (HLEM) methods are used to locate potential fractures on a local scale as a basis for rational borehole siting. The methods, applied separately or in combination, offer an economical approach for use in rural and community water supply, small-scale irrigation and water resources planning. The methods appear to be generally transferable to fissured hard rock aquifers in other regions. The best suited settings are believed to be on cratons and platforms in a semi-arid climate.