Geoelectrical Assessment of Groundwater Potential and Aquifer Protective Capacity Using Vertical Electrical Sounding in Osin-Ekiti, Southwestern Nigeria

Abstract

Adequate supply of potable water is needed for domestic and agricultural uses, and groundwater is a significant source of fresh water that needs to be protected to safeguard its future sustainability. This study utilized the geoelectrical parameters obtained from Vertical Electrical Sounding (VES) to assess groundwater potential and protective capacity of aquifers in parts of Osin-Ekiti, Southwest Nigeria. Sixteen (16) VES points were occupied using the Schlumberger electrode array, with current electrode separation (AB/2) between 1 and 100 m. The geoelectric interpretation identified three to six subsurface layers, comprising topsoil, clay, weathered layer, partly weathered layer, and fresh basement. The resistivity data were interpreted to produce isopach, isoresistivity, and Dar-Zarrouk parameter maps, including longitudinal conductance (S), and transverse resistance (T). Results show that overburden thickness ranges between 1 and 29.1 m, while resistivity values vary from <100 to >19,000 Ωm. The longitudinal conductance values (0.0001–1.6 S) classify the aquifer protective capacity from highly protected to poorly protected, whereas transverse resistance values (<100 to >3000 Ωm²) reveal low to high groundwater potential. The north-central and parts of the central region of the study area exhibit the most favorable conditions with T > 500 Ωm², S ≥ 0.1 S, and appreciable overburden thickness (> 12 m) that indicates a combination of adequate groundwater storage, moderate to high transmissivity, and fair to high aquifer protective capacity.