Subsurface Investigation within Quaternary Alluvium Formation Using Electrical Resistivity Imaging in Birnin Kebbi, Northwestern Nigeria
Adamu, A, Sunusi, Y.A and Abubakar, A.S
Keywords: 2D Electrical Resistivity Imaging (ERI), Quaternary alluvium, Wenner Configuration, ABEM Terrameter and Birnin Kebbi Metropolis.
2D Electrical Resistivity Imaging (ERI) was carried out with the aim of characterizing subsurface layers in order to delineate the alluvium cover within the quaternary formation in Birnin Kebbi and its environs. The objective of this paper is to demonstrate the applicability of the Electrical resistivity imaging (ERI) for mapping of subsurface system within the area of study in terms of layering and layer thickness. Five profiles were occupied in the study area. For each profile, two reels of cables were laid collinearly with 5 m intervals between the outermost electrodes. Each reel had 21 outermost electrodes. However, the two innermost electrodes of the two reels of cables were connected together, thus yielding effectively 42 electrodes and a special length of 200 m. The data obtained using ABEM Terrameter SAS 1000 with electrodes selector were processed using RES2DINV software. The results of this survey in correlation with borehole data revealed four distinct layers: the Lateritic clay (Topsoil) which is about 1.83 to 2.00 m and between 35 to 55 m thick having a resistivity ranging 63.4 Ωm – 91.7 Ωm, the second layer which is a lateritic layer, Sandy Clay (soft overburden) with apparent resistivity ranging from about 112.35 Ωm, to 582 Ωm, occurred at depth ranging from 0 to 19.4 m, the weathered basement is the third layer and has apparent resistivity range of between 582 Ωm to 712 Ωm, fresh basement with apparent resistivity values > 700 Ωm occur at the base of this profile at depth of about 33.4 m at a lateral distance of 150 m along the profile. It can be concluded that the 2D Electrical Resistivity Imaging used in this research (i.e. ERI) are useful and powerful technique for mapping the subsurface and aquifer systems within the quaternary alluvial formation, and in other similar areas.