Delineation of Near-Surface Structural Features Suitable for Groundwater Accommodation Using 1-D and 2-D Resistivity Methods in Igarra, Akoko-Edo, Southwestern Nigeria

A.S Salami,E.M Babafemi

doi:10.4314/jasem.v24i7.13

Abstract

Electrical resistivity methods using dipole-dipole and Schlumberger configurations of Vertical Electrical Sounding (VES) were carried out to evaluate the near-surface structural and lithological features suitable for groundwater development in parts of Igarra, Southwestern Nigeria. Two profiles with lengths of greater than 350m were carried out. A total of fifteen sounding locations along the profile lines were occupied. Dipole-dipole data were interpreted using DiprofWin software while interpretation of the VES data followed two stages of qualitative and quantitative data interpretation using Resist software. Dipole-dipole interpretation results indicate the occurrence of local fractures while VES interpretation results reveal the typical basement rock profile ranging from topsoil, lateritic sand, weathered front, fractured to fresh basement. The significant variations in terms of persistence and thicknesses of these basement vertical rock profiles were revealed by the geoelectrical correlation panels, which indicate typical basement inhomogeneities over short distances. The local structural domains, the weathered front (where thick) and the fractured basement are demonstrably potential sources of groundwater, at least for domestic and small scale enterprises in this part of Igarra.  Keywords: 2-D Pseudosection, Dipole-dipole, Fracture Basement, Vertical Electrical Sounding

Highlights

Igarra and environs are underlain by crystalline basement rocks and groundwater is usually contained in the weathered or fractured basement rocks, and near-surface features of hydrogeological significance
Schlumberger (VES) and Dipole-Dipole arrays widely used for 1-D and 2-D electrical resistivity surveys were employed in this work in order to delineate zones that could serve as sites for groundwater accumulation, which is considered today as the largest available reservoir of fresh water, (Adepelumi, et al, 2013)
Dipole-Dipole: The results of the Dipole-dipole traverses are presented with three 2-D pseudosections for each traverse

Summary

Introduction

Igarra and environs are underlain by crystalline basement rocks and groundwater is usually contained in the weathered or fractured basement rocks, and near-surface features of hydrogeological significance. The apparent resistivity values obtained were plotted on a depth section along intersecting 45° beneath the centre of the dipoles (Figure 4). The first dipole-dipole carried out along Bokeshimi Street (Figure 5) generally has near-surface low resistivity values except between 20-30m (horizontal scale) on the interpreted inverted 2-D pseudosection.

Results

Conclusion