HYDROGEOPHYSICAL INVESTIGATION OF EMURE-EKITI, SOUTHWESTERN, NIGERIA.

Abstract

The Electrical Resistivity Sounding method has been adopted in the mapping of Emure Ekiti with a view to determine the groundwater potential of the community. Eighty three (83) vertical electrical soundings (VES) locations were occupied utilizing the Sclumberger electrode configuration, H and HA curve types were the most dominant sounding curves found within the study area. Three (3) to six (6) subsurface layers identified are the topsoil, laterite, clayey sand, sandy clay, fractured basement and the fresh bedrock. The topsoil resistivity values vary between 42 and 4965 Ω-m, while the thicknesses vary between 0.4 and 2.1 m. The lateritic layer resistivity values vary between 12 and 5772 Ω-m, the thicknesses range between 0.7 and 30.5 m. The clayey sand/sandy clay layer resistivities vary between 42 Ω-m and ∞, while the layer thicknesses also vary between 2.9 and 63.4 m. The fractured basement layer resistivity value also range between 112 Ω-m and ∞, the layer thickness varies from 8.1 and 95.1 m. The weathered layer gave resistivity value between 145 and 16100 Ω-m and the layer thicknesses 61.5 m and ∞. The fresh bedrock resistivities range between 1537 Ω-m and ∞. Combinations of the weathered and fractured basement constitute the aquifer unit in the study area. Geo-electric sections, maps and tables were generated from the interpretation results. Depths to fresh bedrock in the study area range between 0.4 and 132.4 m, whereas the basement relief map reveals fairly deep basement depressions on the northeastern flank of the study area. Basement ridges were delineated on the southwestern flank of the town. On the basis of the geoelectric parameters and maps the study area is therefore classified into poor/low, medium and high groundwater potential zones. The study revealed that 80% of the town area is underlain by marginally thick overburden thus constituting shallow aquifer units with poor to marginal groundwater potential. Partially weathered/fractured basement were delineated in isolated areas with the tendency for low to marginal groundwater yield around the northeastern flank of the town. The results reasonably provide basic information that is expected to assist in the future development of groundwater resource of the town.