An initial estimate of depth to groundwater across Africa

This work aimed to provide an initial estimate of depth to groundwater across Africa, to help with considerations of the applicability of different hand pump technologies in Africa. The main findings and outputs from the work are summarised below: Developing an estimate of depth to groundwater across Africa – In the absence of much observed groundwater-level data in Africa, several modelling approaches were used to estimate depth to groundwater in GIS (refer to section 2.4) using continent-scale datasets of geology, geomorphology and rainfall. Based on comparison to the available observed data, the most successful method was an empirical rule based approach, where depth to groundwater was assigned according to rainfall and aquifer type. Depth to groundwater – Across much of central, western and eastern Africa, where the climate is wet or seasonally wet and basement geology predominates, natural groundwater-levels are generally shallow – approximately 0-25 mbgl. Shallowest groundwater-levels (250 mbgl) are mapped in the major sedimentary basins in north Africa where average annual rainfall is low and aquifers are generally hundreds of metres thick. Expected drawdown – At a pumping rate of 5 m3/d, which is equivalent to that of a hand pump, drawdown is small (1 m2/d. However, where transmissivity is <1 m2/d, drawdown rapidly becomes limiting. This is as a result of the inverse power relationship between transmissivity and drawdown. Transmissivity of