Abstract
<title>Abstract</title> <p>Groundwater occurrence in crystalline basement terrains is restricted to secondary porosity features such as weathered zones and fractures, making exploration challenging. This study presents an integrated geophysical assessment of aquifer geometry and groundwater potential within the basement complex terrain of Osun State University campus, Osogbo, Southwestern Nigeria. Six Vertical Electrical Sounding (VES) surveys using the Schlumberger array (AB/2 = 1-100 m), six Self-Potential (SP) profiles (100-m traverses), and constant-rate pumping tests (120 minutes; 36.7–45.2 L/min) were conducted. VES data were inverted using iterative optimization (RMS < 5%), and SP data were analyzed to identify groundwater flow anomalies. Results revealed 3–4 geoelectric layers: topsoil, lateritic clay, weathered basement (aquifer zone, 3.8–23.3 m thick, 30–171 Ωm), and fresh/fractured basement. The highest groundwater potential occurred at the Engineering Building (VES 4) with a thick, low-resistivity saturated weathered layer (15.7 m, 30 Ωm) underlain by fractured basement (418 Ωm), and a very strong SP anomaly (+ 700 mV). SP anomalies ranged from − 180 to + 700 mV. Aquifer tests revealed specific capacities of 6.02–7.93 L/min/m and transmissivity of 9.4–12.4 m²/day. A strong positive correlation (r = 0.71, p < 0.05) between SP anomaly magnitude and specific capacity confirms that SP responses reflect active groundwater movement rather than merely saturated conditions. The integrated VES-SP approach proved more reliable than either method alone, as VES delineated storage capacity while SP identified permeability. This study provides a cost-effective framework for groundwater exploration in crystalline basement terrains, demonstrating that targeting zones with thick, low-resistivity weathered layers and strong positive SP anomalies significantly improves borehole siting success rates.</p>