Groundwater Potential Assessment of Iwaro-Oka, SW Nigeria Using Geoelectric Parameters

Geoelectric investigation of Iwaro-Oka, SW Nigeria was carried out with the aim of evaluating its groundwater potential for future groundwater development. The area is underlain by Precambrian Basement Complex of southwestern Nigeria with local geology essentially made up migmatite gneiss. Thirty-nine (39) Vertical Electrical Soundings (VES) using Schlumberger configuration were acquired. The VES curves were interpreted quantitatively using partial curve matching and computer assisted 1-D forward modeling. Three distinct geologic layers were delineated within the area. These are topsoil, weathered layer and basement rock. The topsoil is generally thin with no hydrogeologic significant. The weathered layer constitutes the major aquifer unit with thicknesses generally less than 10 m. This layer is predominantly composed of clayey material with resistivity values generally <100 ohm-m. The permeability is low with tendency for low groundwater yielding capacity. The overburden thicknesses vary from 1.1 to 23.5 m but are generally less than 10 m. The fracture density in the area is very low. Out of the thirty-nine VES stations occupied within the area, none show evidence of a fractured basement. The groundwater potential rating of the study area is classified as of low based on relatively thin and clayey aquifer unit.