Geological and Geoelectrical Investigation of a Proposed Dam Site Using Vertical Electrical Sounding at Osuworowo Stream, Utughughu Arochukwu, South Eastern Nigeria

Abstract

Geophysical studies was carried out at a proposed dam site across Osuworowo stream in Arochukwu, south eastern Nigeria to investigate the depth to bedrock, possible geologic structures and foundation conditions of the dam axis.  The study area is located between latitudes 5°23.58”N and 5°23.707”N and longitude 7°53.93”E and 7°53.97”E. Its elevation ranges from 90 ft to 149 ft. Six Vertical Electrical Soundings (VES) were carried out along the stream course using ABEM SAS 1000 TERRAMETER and this was done using Schlumberger configuration with maximum half current electrode separation of 55m able to reveal deep seated structures. The ip2win software was used to model the VES data to give resistivities which vary between 258 Ωm and 39000 Ωm with three and four geoelectric layer combinations of sand, sandstone, sandyshale, shalysand and ale units. The high resistivities of the geoelectric layers sand thickness and dip showing high gradient in elevation differences are indications that the site is suitable for the dam construction. The geological result shows the presence of faults this is confirmed by change in strike and dip.