Investigating Internal Geometry of a Flood plain in Basement Complex Terrain of South-western Nigeria using Electrical Resistance Tomography

Abstract

The subsurface internal geometry of Odo Oba river flood plain located southwest of Ogbomoso southwestern Nigeria was investigated employing Electrical Resistivity Ground Imaging (ERGI) technique using Wenner array. The depth profile of the plain was obtained using Schlumberger array while seven pits were dug along the profiles to ground truth the interpreted results. Interpretation of the inverted apparent resistivity sections indicated a more resistive material (dry sand bodies) with resistivity ranging between 500 Ωm and 2000 Ωm abounds in the study area. Low resistivity (<100 Ωm) observed on some of the profiles is an indication of clay material sandwiched between the sand bodies. The lithology profiles obtained from the pits indicated three distinct layers comprising fine sand, coarse sand and clay. In most cases, the clay is sandwiched between sand bodies within the flood plain. The result of the VES showed a system of three geoelectric layers. This has been interpreted as topsoil, clay and weathered basement.  The strong correlation between the lithology profile obtained from the pits, and interpreted results of the inverted apparent resistivity section has demonstrated the efficacy of electrical resistance tomography as a remarkable geophysical tool for detecting and delineating resistive bodies buried in conductive sediments.