Groundwater development in a mixed geological terrain: a case study of Niger State, central Nigeria

Abstract

Groundwater occurrence and characteristics of Niger State, Nigeria was studied using a combination of geological, hydrogeological and geophysical survey methods. Geological studies involved a determination of the various rock types and lithology, hydrogeological investigations involved the use of water levels in open hand dug wells and boreholes, while geophysical survey methods involved the use of electrical resistivity methods to determine subsurface conditions. The state is basically underlain by crystalline and the sedimentary rocks occurring in equal proportion. The crystalline rocks comprises mainly of granite, gneisses, migmatite and schist while the sedimentary deposits are mostly made up of sandstone, clays and shale. Groundwater occurs in the area in three broad categories; fractured/weathered aquifers in hard rock terrain, sandstone/grit aquifer in the sedimentary rock terrain and sandstone/conglomerate/ fractured rock in geologic contact areas. Groundwater yield varies widely in the three categories. Shallow sedimentary aquifers have the highest yield of about 1.4–2.8 lt/s (120– 241 m3/d), granite/gneiss/migmatite have a yield of 0.8–1.8 lt/s (70–155 m3/d) groundwater in the schist is low (below 0.6 lt/s) and sometimes wells placed in them are non-productive. Groundwater yields in the geologic contact areas vary from very low, where non fractured rock is overlain by clay, while very high yield is obtained in areas where the contact point is represented by conglomerate. Groundwater development in the state can best be achieved through a combination of geological, hydrogeological and geophysical survey methods.