Application of electrical resistivity survey for groundwater investigation in a basement rock region: A case study of Akobo - Ibadan, Nigeria

Abstract

A geo-resistivity exploration has been carried out for groundwater within the Akobo catchment of the ancient city of Ibadan. The area lies within the basement rock terrain of South Western Nigeria and bounded by  longitudes 3^o 51′ – 3^o 53′E and latitudes 7^o 22′ – 7^o 24′N. The exploration was done using SYSCAL KID meter while a total of 10 VES with an average of 46m station interval were completed in 3 profiles by means of Schlumberger configuration with total current electrode spread of 160m. The results revealed that the area is underlain by four geo-electric layers. The top lateritic soil has resistivity values ranging from 28.1 to 481.8 Ωm and thickness of 0.8 to 5.7m. The second layer has sand/clay intercalation with resistivity values varying between 47.7 and 192.5 Ωm and thickness varying between 2.8 and 19.4 m. The weathered/fractured basement has resistivity values from 106.2 to 846.8 Ωm with thickness of 13.2 to 24.9m while the partly weathered/fresh basement layer has resistivities ranging
from 130 to 856.4 Ωm. The distribution of resistivities in the area shows that the weathered basement has a relatively low resistivity (< 200 Ωm) values in the north-eastern and north-western axis coupled with high thickness values (> 20 m) which suggests the presence of an aquiferous zone. Therefore, this portion of the study area could be highly hydro-geologically promising and maybe recommended for siting groundwater tube.

Key words: Geo-resistivity, groundwater, basement rock, borehole and Ibadan