Hydrogeophysical exploration of groundwater potential in southwestern basement terrain of part of Ago-Iwoye, South western Nigeria.

Abstract

Electrical resistivity survey of Ago-Iwoye southwestern Nigeria was done with the aim of delineating potential zones for groundwater exploitation. The rock types present are mainly gneissic rocks; granite gneiss, banded gneiss, biotite gneiss and porphyroblastic gneiss.Forty five (45) Vertical Electrical Soundings (VES) of schlumberger array were carried out using maximum electrode spacing (AB/2) of 100m. The results obtained were interpreted using partial curve matching which serves as model input for the computer iteration using WINRESIST software to determine the resistivity, thickness and depth of each layer in the subsurface. The identified curve types are H, KH, HKH, A, K and QH types while the H type curve is predominant. The three prominent geo-electric layers were inferred, these are the topsoil, weathered layer (sand/clay/clayey sand) and fresh/fractured bedrock with resistivity values of 33.4Ωm - 2266.3Ωm, 8.3Ωm - 1106.3Ωm and 68.4Ωm - 21729.6Ωm respectively. The isopach reveals overburden thickness range of 2m – 52m, bedrock resistivity ranges from 1000Ωm - 19000Ωm and reflection coefficient range from 0.62 -0.92.The study area is predominantly of low yield but areas in the northeastern and western part of the study area have high aquiferous groundwater potential areas are only noticeable in the northeastern and western part of the study area.