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Groundwater potential in Sierra Leone

Groundwater is a major source of safe drinking water  throughout Africa. Despite this, little quantitative information on aquifers potential is known in many countries. Sierra Leone has annual precipitation rates of as much of 5000 mm/yr and a capillary net of surface streams, but the hydrogeological aspect was never taken into serious consideration. Between 2016 and 2017, Hydro Nova (USA) conducted an extensive survey on all existing hydrogeological data in the country. The flagship product of this study was the Hydrogeologic Atlas of  Sierra Leone, a series of 20 maps complemented with textual notes, published in official digital and hardcopy formats.  The project showed that the majority of the 28900 wells, from the national survey, are located in unconfined aquifers of limited extent and of three different types: perched, along large river banks, porous, widely distributed across the country and along the coast and fractured, in the crystalline basement. The latter are generally deep and underlying the surface formation in the lateritic soils. The water table flows from NE to SW following the main water courses and is generally correlated to the topography.  The crystalline basement is the common layer at the bottom of the aquifer at depth of 15-80 m. Well yield is normally in the range of 0.3-1.5 l/s and exceptionally 3-6 l/s. Transmissivity is also low (2-3 m2 /d). As a consequence many boreholes must remain unpumped, for some hours, to recover an exploitable water level. The entire report and other publications related to this paper can be accessed via the following link: http://www.salgrid.org