Groundwater Prospect Within The Basement Complex Of South-western Nigeria Using Vertical Electrical Soundings

Geophysical investigations involving the use of Vertical Electrical Soundings was conducted across the basement complex rocks with the aim of determining its geoelectric parameters and hydrologic significance. A total of eight (8) vertical electrical soundings were carried out using the Schlumberger array configuration, with half the current electrode separation (AB/2) varying from 1m to 100m. VES were conducted cross the whole study area to obtain information about the subsurface lithologies, overburden thickness and possible basement structures that could harbour the accumulation of groundwater. The geo-electric parameter results obtained from the sounding curves revealed 3-layer, 4-layer and 5-layer earth models, respectively. The 3-layer model has 75% of occurrence, while the 4- layer has (12.5%) and (12.5%) for the 5-layer models. This shows that the subsurface layers can be characterised into topsoil, clay /sandy-clay, weathered/fractured layer, and the fresh bedrock. The weathered and/or the fractured basement are the aquifer types delineated across the area. Depth to bedrock ranges from 0.2m to 8.5m across the study area. On the basis of subsurface parameters and further interpretations of the VES data, assisted in the zoning the study area into moderate and low groundwater potential zones. The investigation revealed that basement depressions mostly constitute high groundwater potential zones in the study area. The study, envisaged to provide a reliable guide on the groundwater potential in the area, is expected to assist in future development of groundwater resources to sustain the water requirements of the community.