PATTERN OF ELECTRICAL RESISTIVITY IN REGOLITH AQUIFER AND THEIR IMPLICATION FOR GROUNDWATER MANAGEMENT IN ILORIN METROPOLIS, NIGERIA
Groundwater development in basement complex terrains is largely dependent on the occurrence and characteristics of the regolith aquifer, making geophysical investigation a vital precursor to borehole siting. This paper examines the pattern of electrical resistivity in the regolith aquifer of Ilorin metropolis, Kwara State, Nigeria. Forty (40) Vertical Electrical Sounding (VES) points were established across the study area to delineate subsurface lithological layers, determine resistivity patterns, and estimate weathering depth. The resistivity data were processed and interpreted using computer iteration techniques, while an aquifer potential index was used to evaluate groundwater potential. The findings reveal a geo-electric sequence of five lithological layers, comprising topsoil, lateritic layer, clayey soil, weathered basement, and fresh basement, with resistivity curve types identified as H, K, A, and Q. The regolith aquifer, represented by the weathered basement, recorded resistivity values ranging from 3.57Ωm to 297Ωm, while weathering depth varied from 3.30 m to 31.28 m, with both parameters showing higher values in the south-western and north-eastern parts of the study area. Analysis indicated that 45% of the study area exhibited optimum weathering and groundwater potential, whereas correlation analysis revealed a weak inverse relationship (r = -0.361) between regolith resistivity and aquifer potential, suggesting that resistivity alone is insufficient predictor of groundwater yield. The study concludes that the regolith aquifer constitutes the principal groundwater reservoir in the study area. Recommendations include the adoption of pre-drilling geophysical surveys as a mandatory practice and the prioritization of boreholes in zones identified with optimum aquifer potential.