Aquifer characterization of some parts of Ijebu Igbo using electrical resistivity methods

Abstract

Groundwater aquifer mapping is a scientific process, where-in a combination of geologic, geophysical and hydrologic analyses are applied to characterize the quantity, quality and sustainability of groundwater in aquifers. A total of ten (10) Vertical Electrical Sounding (VES) and six (6) two dimensional (2-D) Electrical Resistivity Tomography (ERT) lines were achieved. The 2-D ERT lines were carried out on a length of about 240 m – 320 m using Dipole-dipole electrode configuration. Acquired 2- D and VES data was processed using RES2DINV and WINRESIST software respectively. The VES results obtained showed that the study area has 3 to 4 geoelectric layers with the following lithology namely; the topsoil, partially weathered, fractured layer and the fresh bedrock. The topsoil has a resistivity value of about 609 Ωm. The thickness and the depth representation of weathered basement and fractured basement vary from one another. They have a resistivity value of about 128 Ωm and 1089 Ωm respectively. The 2-D inverse models obtained from the area showed the presence of vertical contacts and fractured zones that can serve as an aquifer for the surveyed area. The pseudosection of the inversion results unravel the two profiles with saturated fractured basement where adequate groundwater can be obtained. The Iso-Pach map showed high contour closures which are good signature for good to moderate groundwater potential zones on profiles four, five and six (VES 7,8 and 9). In contrast, profiles one, two, three (VES 2 and 6) displayed low closures which depicts low overburden thickness and categorically means poor groundwater potential zones.