Geoelectric Sounding for Evaluating Soil Corrosivity and the Vulnerability of Porous Media Aquifers in Parts of the Chad Basin Fadama Floodplain, Northeastern Nigeria

Abstract

A geoelectrical survey was carried out in parts of the Chad Basin Fadama Floodplain as a means of evaluating both the soil corrosivity and protective capacity. One hundred and six Schlumberger Vertical Electrical Sounding data were collected at the corners of a 225 x 225 m square grid network. Topsoil resistivity and topsoil longitudinal unit conductance maps were generated from the first and second order geoelectric parameters respectively. Areas considered as high corrosivity are the north central, southwestern, southern and northern parts with (r<180w-m). Part of the study area characterized by materials of poor to weak protective capacity has longitudinal conductance values of less than 0.1 and (0.1 - 0.19) mhos respectively. Values between (0.2 - 0.79 mhos - sandy clay cover) and (0.8 - 4.9 mhos - clay cover) correspond to moderate and good protective capacity respectively. It can thus be concluded that the flanks of the floodplain underlain by appreciable clayey topsoil thickness columns are susceptible to corrosion tendency. These same flanks are characterized by materials of moderate to good protective capacity and serve as sealing potential for the underlying hydrogeological system in the area.