Geophysical investigation has been undertaken at an existing dam site within the main campus of University of Ilorin, located around the southern flank of the Nigerian basement complex in West central part of Nigeria. This is aimed at evaluating the geo-structural setting of the concealed bedrock, the fracture pattern and possible dam seepage along the dam axis and its banks. Vertical Electrical Sounding (VES) technique of Schlumberger electrode configuration method was used for the field study. Twenty seven VES stations on eight profiles were established along the West-East flank of the dam. The three major lithologic units delineated are the topsoil, weak/gravelly zone and the fracture/fresh basement. The geoelectric sections reveal fractured basement beneath 4 stations of which two (i.e. VES 1 and 10) are along the dam reservoir and the two starts at the depth of 10 m, extending downward. The geoelectric maps show high resistivity range of about 29-2613 Ωm and thickness range of 0.8-3.1 m. This is underlain by relatively low resistivity layer whose values loiters around 100 Ωm with thickness range of 1.8-11.3 m, indicating near surface bedrock straddled with basement depression or fracture. The fractured basement and low resistivity zone is considered inimical to the continued water retention or zone of anomalous seepage as there is no surface manifestation and significant water reduction can be experienced. This is considered as responsible for low water retention in the reservoir during the dry season.
