The Geoelectric characterisation of aquifer in Sabon-Gari, Bauchi, Northeastern Nigeria

Abstract

Electrical resistivity investigation using Schlumberger configuration was conducted in Sabon-Gari, Bauchi, Bauchi State Nigeria. The study area is situated between 10.399°N to 10.410°N and 009.815°E to 009.825°E within the Basement complex of Nigeria. Because of a good number of failed wells and boreholes in the area, there arises a need to carry out a geophysical study to characterise the underlying aquifer system. A total of twenty-five vertical electrical soundings (VES) were carried out with a maximum electrode spacing of 300 m (i.e. AB/2=150 m). Analysis of the acquired sounding data revealed a three-to-four geoelectric layer formations; topsoil, highly weathered, weathered, and fresh basement rocks as correlated with existing borehole data. Assessing the groundwater potential, thickness and resistivity of the unconsolidated overburden materials is the focus. The overburden thickness varies from 1.9 to 27.8 m where about 60% of it falls within the 1.9 m to 10 m bracket; thus indicating  its thinness. The aquifer thickness varies within 1.5 to 25.4 m range.  The aquifer resistivity varies from 7.5 to 373 Ωm, and this information was used to determine the aquifer’s transmissivity, calculated to range from 18.2 to 275 m²/day. The aquifer unit in the study area, therefore, shows a generally low to medium groundwater potential. The longitudinal conductance of the geoelectric topmost layer across the area was also used to assess the vulnerability of the underlying aquifer to near-surface contaminants. The aquifer is found to be of moderate to poor protective capacity rating. The general indication over the study area is that wells and boreholes fail because of its general low groundwater potential and poor borehole siting. This could be addressed by designing wells based on water flow and avoiding areas with low potential.