Groundwater Potential Evaluation Using Electrical Resistivity Method at Laniba, Ibadan, Southwestern Nigeria

Abstract

A geophysical investigation involving an electrical resistivity method using Vertical Electrical Sounding technique has been carried out at Laniba, Ibadan, falling within the Precambrian basement complex of Southwestern Nigeria. This was aimed at characterizing the subsurface geoelectric sequences and evaluating the groundwater potential of the area for groundwater development. A total of Ten (10) Vertical Electrical Sounding (VES) was conducted out across the area using Schlumberger array with a maximum half- current electrode separation of 100m using Ohmega Resistivity Meter. The field data obtained was plotted using bi-logarithm graph and interpreted quantitatively by partial curve matching technique and computer iteration using WinResist Software. The interpretation of the VES data reveals three to four geo- electric layers, based on characteristic resistivity ranges, comprising of topsoil, lateritic soil/clayey soil / Quartzite and Quartz- Schist formation, weathered basement and fractured basement with resistivity of 46- 1024 Ohm-m, 91-3369 Ohm-m, 55-365 Ohm-m and 338-886 Ohm-m respectively. Their thickness respectively varies from 2.2-16.6m, 0.6-14.4m and 14.7-46.5m. Two probable aquiferous units namely; weathered basement and fractured basement have been delineated based on the observed resistivity values. The groundwater potential map produced by integrating various categories of aquifer maps classified the area into poor, fair, moderate and good groundwater potential zones with about 60% of the area characterized by moderate to high groundwater discharge. Hence, groundwater development is feasible in the area; mostly where both aquiferous units delineated exists. The Vertical electrical sounding technique of electrical resistivity method employed has been efficient in evaluating the groundwater potential of the area.

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