Lineament-Density-Guided Vertical Electrical Sounding for Geoelectric Characterization and Groundwater Potential Mapping of a Basement Complex Terrain, Southwestern Nigeria

<title>Abstract</title> <p>Groundwater development in Precambrian basement complex terrains depends on locating zones of fracture-enhanced secondary porosity, which are difficult to target without invasive drilling because primary basement rocks have negligible intrinsic porosity and permeability. This study reports a lineament-density-guided vertical electrical sounding (VES) survey designed to validate a structural favourability model derived independently from Landsat-8 remote sensing and aeromagnetic lineament mapping (reported in a companion paper) across the Adekunle Ajasin University campus, Akungba-Akoko, southwestern Nigeria, a site with a documented history of low-yield and failed boreholes. Twenty Schlumberger-array VES stations (AB/2 up to 100 m) were sited at lineament intersections spanning very-low to very-high composite lineament-density classes, and apparent resistivity data were interpreted through partial curve matching followed by WinResist iterative inversion. The results delineate three-to-four-layer geoelectric sequences (topsoil, weathered layer, fractured/weathered basement, and fresh basement) with resistivities ranging from about 47 Ω·m in clay-rich weathered zones to in excess of 40,000 Ω·m in unweathered basement and a locally intercalated quartzite body, interpreted basement depths of approximately 6–74 m, and curve types dominated by the H, HA, K and KH families (H/HA-type curves account for 45% of stations and are concentrated in high lineament-density corridors, while K/A-type curves account for 40% and dominate low-density zones). To quantify aquifer protective capacity, Dar-Zarrouk longitudinal conductance (S) and transverse resistance (T) were computed from the reported layer parameters for all twenty stations; S values are predominantly in the weak-to-poor protective-capacity class (0.002–0.229 mho, with one moderate-to-good outlier at VES 18, S = 0.549 mho), consistent with the generally thin, sandy, poorly clay-rich overburden typical of actively weathering basement terrain. Stations located within high-density lineament corridors coincide with thicker weathered/fractured zones and comparatively higher transverse resistance, classified as moderate-to-good groundwater prospects, whereas stations in low lineament-density zones show thin overburden directly overlying resistive, largely unfractured basement, classified as poor prospects; this pattern is consistent with the known spatial distribution of productive versus failed boreholes on campus. The findings support composite lineament density, derived from independently acquired remote sensing and aeromagnetic data, as a practically useful first-pass siting criterion for borehole and engineering-foundation investigations in comparable basement complex settings, while underscoring the continued necessity of direct geoelectric verification, explicit inversion-quality reporting, and aquifer protective-capacity assessment before final site selection.</p>