An integration of aeromagnetic and electrical resistivity methods in dam site investigation

Abstract

Aeromagnetic map (Katsina-Ala sheet 272 S.E.) and the electrical resistivity sounding data obtained along eight traverses, from two sites, across the Katsina-Ala river were examined with the principal aim of defining depths to the bedrock, bedrock relief, geologic structures and the nature of the superficial deposit. The purpose of this exercise was the selection of probable axis for a hydroelectric power dam. The aeomagnetic map shows the basement rocks trending roughly NE-SW. This trend correlates with the 40°–45° strike of foliation measurements made on the rock outcrops along the river channel. A network of cross cutting lineaments suspected to be fault/fractures trending approximately NE/SW and NW/SE was delineated from the magnetic map. The depths to the bedrock estimated from depth sounding data at site I generally vary from 1–53.1 m. Depths to the bedrock estimated at site II range from 1.9–19.5 m. The superficial deposit varies from clay to sandy clay. clayey sand (with boulders in places), sand and laterite. The bedrock relief is relatively flat and gently undulating along most of the traverses with an overall dip towards the river channel. Except for the relatively high overburden thicknesses, two traverses at site I and one traverse at site II are probable, axes for a major and minor dam respectively.