Estimation of natural direct groundwater recharge in southwest Ghana using water balance simulations

The Sacramento soil moisture-accounting model has been used to simulate the discharges of a major catchment (Pra river basin) in southern Ghana. Through the simulation it was possible to assess the temporal variability of evapotranspiratio, base flow proportions and groundwater in storage, as well as the average groundwater recharge to the weathered aquifers. Groundwater recharge was estimated by considering the measured discharge of groundwater across the boundary of the basin over periods of equivalent storage, to be equal to the net recharge inside the catchment. The direct groundwater recharge rate over the basin of area 22,836 km2 amounted to an annual average of 50 mm. This represented 4 % of mean annual rainfall of 1300 mm, giving natural groundwater resources potential of 1.6 l s-1 km-2. For regional groundwater resources assessment, the results obtained could be applied to other river basins in southwest Ghana.