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

Aeromagnetic map and electrical resistivity sounding data obtained along eight traverses were examined at two sites across the Katsina‐Ala River. The principal goals of this exercise were to define depths to the bedrock, bedrock relief, geologic structures, define the nature of the superficial deposit, and select probable minor and major axes for hydroelectric power dams. The aeromagnetic map shows that the basement rocks trend roughly northeast‐southwest, which correlates with the strike of foliation measurements made on rock outcrops along the river channel. A network of cross cutting lineaments, suspected to be faults/fractures that trend approximately northeast/southwest and northwest/southeast, was also delineated from the magnetic map. The depths to the bedrock estimated from resistivity 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, to clayey sand (with boulders in places), and to sand and laterite. The bedrock relief is relatively flat and gently undulates along most of the traverses, with an overall dip towards the river channel. Traverses E-F or I‐J at site I and K-L at site II are probable dam axes. These traverses are characterized by relatively thin overburden thicknesses and rock heads dipping toward the river channel, thereby reducing the likelihood of water seepages from the flanks of the proposed dam axes.