Shallow Aquifer Assessment Using Resistivity Methods in Gem Local Government Area, Kebbi State, North West Nigeria

Rural communities in Gem Local Government Area of Kebbi State experience seasonal water shortages due to the dependence on shallow unconfined aquifers in crystalline basement terrain that are recharged primarily by intermittent rainfall. This study assesses the productive potential of shallow aquifers using a combination of vertical electrical sounding and two-dimensional resistivity profiling. Twenty-two VES stations and two 400-metre resistivity profiles were acquired across a 30-square-kilometre area to characterise the weathered basement aquifer. VES data were interpreted using partial curve matching followed by computer-assisted inversion, yielding a three-layer model at most stations comprising lateritic topsoil, weathered basement, and fresh basement. Geoelectric parameters derived from the layer models, specifically the longitudinal conductance values, are used to evaluate the protective capacity of the overburden against potential contamination of the aquifer. Resistivity profiling reveals a NW-SE trending zone of relatively deep weathering extending to 20 metres, coinciding with an inferred shear zone mapped in regional geological literature. Aquifer thickness in this zone is estimated at 8 to 15 metres with estimated hydraulic conductivity values between 0.5 and 3.5 metres per day based on empirical correlations. Three optimal borehole sites are identified and mapped. The study provides a reliable hydrogeophysical database for community water supply planning in the area. Keywords: VES, shallow aquifer, Kebbi State, weathered basement, geoelectric parameters