Geoelectric Characterization of Aquiferous Units and its Implication on Groundwater Potential of Owo, Southwestern Nigeria

Abstract

Geophysical study of the North-eastern part of Owo was conducted to investigate the geoelectric characteristics of its aquiferous units and its implication on groundwater potential of the area. Vertical electrical sounding method was employed and Schlumberger configuration was adopted. Thirty-two points were sounded along three different sections of the town namely; Idasen, Okedogbon and Express (Figure 1). Six different subsurface lithologic units were established namely; lateritic topsoil, clay, sand, quartzite, weathered/fractured basement and, basement. The curve types range between simple H, K, HA, HK, KH to complex, HKH, KHA and KHK. The topsoil, clay, sand and weathered basement materials are characterised with relatively low resistivity values while the quartzite ridge materials are characterized with high resistivity values. The average resistivity and thickness values for the topsoil are 220 Ωm and 2.0 m respectively. Clay was encountered across Okedogbon and Express area of the town and the average resistivity and thickness values of 34 Ωm and 6.0 m respectively. Sand was encountered across the entire study area with average resistivity and thickness values of 115 Ωm and 11.0 m respectively. Quartzite was encountered in all the locations with average resistivity and thickness values of 611 Ωm and 11.0 m respectively. Weathered/fractured basement was encountered across the three sections with average resistivity and thickness values of 86 Ωm and 12.0 m respectively. Basement is relatively deep in the study area and the average resistivity and depth values to the top of basement are 878 Ωm, and 24 m respectively. Overburden thickness was established across the area with an average value of 20 m. The overburden materials with the fractured basement constitutes aquiferous units within the study area though the sand and weathered basement units are largely responsible for the groundwater potential. The groundwater potential of the area is moderate with Express area having the highest potential.