Estimates of the relative specific yield of aquifers from geo-electrical sounding data of the coastal plains of southeastern Nigeria

Abstract

This paper discusses a method of estimating aquifer specific yield based on surface resistivity sounding measurements supplemented with data on water conductivity. The practical aim of the method is to suggest a parallel low cost method of estimating aquifer properties. The starting point is the Archie's law, which relates porosity and degree of saturation to electrical resistivity derived from geoelectrical field curves. Geoelectrical sounding using the Schlumberger electrode array were conducted in the Njaba River sub-basin covering an area approximately 575km². The Njaba River sub-basin is underlain by the Coastal Plain Sands (Benin Formation). The formation is made up of very friable sands with minor intercalations of clay. The data were interpreted to obtain the layer resistivities of the saturated and unsaturated zones. Porosity and degree of saturation and hence the specific yield were estimated from the electrical resistivity according to Archie's law. In spite of the uncertainties that exist in the relationship between resistivities and porosity and degree of saturation due to the generalized assumption on the material constants in Archie's law, the values of the specific yield obtained with the suggested geophysical method agree well with the values obtained from aquifer test in the study area. This study gives an insight into the groundwater potentials of the study area.

Nigerian Journal of Technology and Education in Nigeria Vol. 8(1) 2003: 69-83