Integrated Geophysical Survey for Mapping Aquifer Parameters in Sokoto Basin

This study integrates electrical resistivity and electromagnetic methods to map aquifer parameters in the Sokoto Sedimentary Basin, Sokoto State, North West Nigeria. The Sokoto Basin contains regionally significant aquifers in the Paleocene Kalambaina limestone and the Eocene Gwandu Formation that supply domestic and agricultural water to millions of people in the Northwest. Increasing population pressure, agricultural expansion, and climate-driven recharge reduction require improved understanding of aquifer spatial variability to guide rational groundwater management. This study acquires 36 Schlumberger VES stations and EM34 apparent conductivity profiles along 6 traverses in Tambuwal, Illela, and Gwadabawa local government areas. VES data are inverted using IX1D to produce multi-layer earth models constrained by available lithostratigraphic logs from the SRWSSP database. EM34 profiles at 20-metre horizontal and vertical dipole separations detect shallow conductors. Correlation of VES layer models with available borehole data validates the interpreted layer assignments. Dar-Zarrouk parameters including longitudinal conductance and transverse resistance are computed from layer models and mapped spatially. Findings reveal a productive limestone aquifer at 20 to 55 metres depth with resistivity values of 40 to 180 ohm-metres, overlain by a regionally extensive sandy clay confining layer of 8 to 18 metres thickness. Longitudinal conductance below 0.1 siemens identifies areas of thin or leaky confinement that are vulnerable to surface contamination. The study recommends prioritising the deeper Gwandu sandstone in areas of inadequate limestone confinement, and provides a spatial aquifer management framework for the surveyed area.

Keywords: aquifer mapping, Sokoto Basin, VES, Dar-Zarrouk parameters, electromagnetic survey.