GROUNDWATER POTENTIAL EVALUATION USING ELECTRICAL RESISTIVITY METHOD IN A TYPICAL BASEMENT COMPLEX AREA OF NIGERIA

Abstract

A geophysical survey employing the electrical resistivity method was carried out within the permanent site of the University of Agriculture, Abeokuta (UNAAB), Ogun state, Southwestern Nigeria. A total of 46 Schlumberger vertical electrical sounding (VES) stations were occupied using the ABEM Terrameter SAS 300B model with maximum inter-electrode spacing (AB) of 200m. The aquifer units are characterized by sand, sandy clay/clayey sand, weathered and fractured rocks. The plot of the aquifer resistivity against the coefficient of anisotropy shows that the basement in the study area is underlain by three types of rocks: Quartzite with aquifer resistivity in the range of 50 – 430Ωm and coefficient of anisotropy between 1.01 and 1.18. This weathered mainly to sand with good to high groundwater yield; Granite-gneiss with aquifer resistivity in the range of 40 – 90Ωm and coefficient of anisotropy of between 1.18 and 1.88. This weathered to a mixture of clay and sand with low to medium groundwater yield; Mica-schist with aquifer resistivity in the range of 16 – 40Ωm and coefficient of anisotropy of between 1.3 and 2.3. This weathered into more of clay because of its high ferromagnetic mineral content and as such has zero to very poor groundwater yield.