Integrating geoelectrical and borehole data in the characterization of basement-rock aquifers in the Lokoja area, northcentral Nigeria

Abstract

The study area is composed of mainly basement rocks, with problems of low yield of groundwater in most of the boreholes drilled. Therefore, this study was carried out to evaluate the hydraulic parameters of the basement aquifers using the vertical electrical sounding (VES), constant rate pumping test, and borehole logs. The mean value of aquifer resistivity and thickness are 408.4 Ωm and 20.2 m. The depth ranges from 20.9-88.0 m with a mean value of 55.5 m; showing appreciable groundwater potential mostly within the southern part. The value of transmissivity and hydraulic conductivity from the resistivity data ranges from 2.058-1761.033 m²/day and 0.205-138.664 m/day with a mean value of 152.251 m²/day and 8.841 m/day, respectively, indicating porous and permeable zones within the southern and northwestern part of the study area. The value of longitudinal conductance and transverse unit resistance ranges from 0.0034-4.2333 m-hom and 38.1-146439 Ωm² with a mean value of 0.3250 m-hom and 9704.1 Ωm²; indicating poor to moderate protective capacity in almost the entire area except for the small portion within the southern part. The mean value of fracture contrast and the reflection coefficient are 0.743 and -0.333, showing that the southern part has more water-filled fractures. Conclusively, this study reveals, that the aquifer depth ranges from 60-90 m, the transmissivity and hydraulic conductivity demonstrate high porosity and permeability within the southern parts of the study area, and serve as a baseline for groundwater resource management policy in Nigeria.