Potential groundwater discharges and safe yields of drainage basins in southwestern Nigeria

The potential safe yields of aquifers in the rocks and saprolites of third-order drainage basins on the Pre-Cambrian Basement Complex of southwestern Nigeria are determined and presented using the Total Potential Groundwater discharge (Q_TP) model of Butler (1957) and Meyboom (1961). The safe yield values range from 22 1 min⁻¹ to 2156 1 min⁻¹. These values compare with those from the Basement Complex in some other parts of Nigeria but most of them appear very low when compared with yields of between 640 and 1740 1 min⁻¹ reported for sedimentary rocks within the same region. The relatively high values of between 642 and 2156 1 min⁻¹ reported in this study were obtained from aquifers located within the highly fissured quartzitic rocks and their associated coarse grained saprolites.

The potential safe yield values from the basins may thus show that apart from those areas underlain by quartzites and such other highly fissured rocks overlain by coarse grained saprolites e.g. porphyritic/coarse grained granites (and these are not widespread on the Basement Complex), the Basement Complex is an area of poor groundwater yield.