Hydrogeophysical study of Ogbese South Western Nigeria

Abstract

A hydrogeophysical study of Ogbese town in Ondo State southwestern Nigeria has been undertaken in this study. Twenty-nine (29) Schlumberger electrical soundings (VES) were carried out with the aim of establishing the groundwater potential of the area. The Precambrian basement complex of southwestern Nigeria underlies the area with the local geology being essentially granite-gneiss and migmatite. The computer-assisted sounding interpretation revealed two distinct geoelectric layers overlying highly resistive basement. These include the topsoil and the weathered layer. The isopach map of the overburden shows depth to the bedrock, which varies from 3 m to 27 m. The relatively thick overburden areas (<15m) were marked T1 and T2. The weathered layer, which is relatively thin with high clay content, constitutes the aquifer units; hence, the groundwater potential of the area is considered to be of low rating. The overburden coefficient of anisotropy (ʎ) values of the area varies from 1.00 to 1.60. The area underlain by migmatite is characterized by relatively high ʎ values (>1.3), while the areas underlain by the gneisses are characterized by relatively low ʎ values (< 1.3). The relatively high ʎ values for migmatite can be explained in term of its broad lithological differentiation. The characteristic longitudinal conductance (range from 0.001 mhos to 0.353mhos) of the area enabled the rating of the overburden protective capacity into moderate, weak and poor. About 70% of the area falls within the weak/poor rating; this suggests a generally weak overburden protective capacity around the study area.