Geoelectrical exploration for groundwater in crystalline basement rocks of Gbongudu community, Ibadan, Southwestern Nigeria

M. A. Oladunjoye,I. A. Korode,A. Adefehinti

doi:10.4314/gjgs.v17i1.3

Abstract

Gbongudu community, Ibadan underlain by crystalline rocks of Basement Complex of Southwestern Nigeria has need for alternative water supply due to inadequacies of surface water supply and common occurrences of low yield or dry boreholes coupled with rapid development within the community. Geophysical investigation involving electrical resistivity was carried out with the aim of evaluating the groundwater potential of the community. Thirty-three (33) Vertical Electrical Soundings were acquired across the community adopting Schlumberger electrode configuration with current electrode separation (AB) varying from 2 to 200 m. The acquired field data were interpreted using partial curve matching with suitable auxiliary chart and “RESIST” resistivity sounding interpretation software was also used for iteration. The results revealed two to five geo-electric layers, namely, topsoil, clayey soil, lateritic clay, weathered layer, fractured unit and fresh basement. The weathered and the fractured units form the aquiferous zones in the area investigated. Thematic maps of geoelectric and Dar-Zarrouk parameters produced from the interpreted VES data are aquifer unit (weathered layer) thickness map, aquifer unit (weathered layer) resistivity map, overburden thickness map, basement resistivity map, basement topography map, reflection coefficient map, total longitudinal conductance map, total transverse resistance map and electrical anisotropy (coefficient of anisotropy) map. The thematic maps were combined to form a single component which gives the groundwater potential map of the study area. The groundwater potential map was used to classify the study area into poor, low and good aquifer potential zones. The study reveals that the weathered and fractured zone that occur in the southeastern part of the study area constitute the water bearing zone which can be regarded as good groundwater potential. This study has provided evidence on the hydrogeologic framework and subsurface nature of main aquifer units in the area.KEY WORDS: Groundwater exploration, RESIST, Dar-Zarrouk parameters, Electrical anisotropy, Borehole drilling.

Highlights

Groundwater is one of the most precious natural resources which determines the health and well-being of people living in any environment
From the final model derived from the software, geoelectric parameters which comprises; overburden thickness, weathered basement resistivity, weathered basement thickness, basement rock topography, basement rock resistivity, resistivity contrast and reflection coefficient were acquired
Thematic map for each geoelectric parameter was generated and integrated which give the groundwater potential map of the area.The basement rock topography was obtained by subtracting the overburden thickness of each vertical electrical sounding (VES) point from elevation of the same point

Summary

Introduction

Groundwater is one of the most precious natural resources which determines the health and well-being of people living in any environment. Groundwater is referred to as the waters found under the surface of ground (Bear and Verruijt, 1987). It is very important because it is the source of water for some communities that they depend on it for domestic, agricultural, and industrial uses. Groundwater is being replenished by rain which infiltrate the soil or through secondary pores of the subsurface rocks (Nampak et al, 2014). The occurrence and distribution of groundwater in an area can be influenced by; climatic condition, geology, the structural features present in the subsurface rock, geomorphological features, land use type and their interplay with the hydrological features (Edetet al., 1998, Jaturonet al., 2014, Kumar et al, 2007).

Methods

Findings

Conclusion