Integrated Geophysical and Hydrogeological Modelling of the Sokoto Rima Basin Aquifer System

This study develops an integrated geophysical and hydrogeological model of the Sokoto Rima Basin aquifer system in North West Nigeria, providing a quantitative framework for sustainable groundwater resource management. The Sokoto Rima Basin is one of Nigeria's most important sedimentary basin aquifer systems, supporting domestic, agricultural, and pastoral water needs across Sokoto and Kebbi States. Progressive water level decline and increasing abstraction require an improved quantitative understanding of aquifer geometry, hydraulic parameters, and recharge processes. This study integrates existing VES data (148 soundings from government and NGO surveys), new ground TEM surveys (36 stations), and available borehole data from the SRWSSP database into a 3D aquifer model constructed using MODFLOW groundwater modelling software. TEM data resolve the deep aquifer structure beyond the practical depth of VES surveys. Aquifer geometry from geophysical interpretation provides the structural framework for hydrogeological model construction. Recharge estimates from water table fluctuation and chloride mass balance methods calibrate the model. Transient calibration uses 15 years of water level monitoring data from 24 observation boreholes. Findings reveal a complex multi-layer aquifer system with the productive Gwandu Formation sandstone extending to 300 metres depth and showing recharge connectivity to the Rima River floodplain. The calibrated model predicts sustainable groundwater abstraction of 1.8 billion cubic metres per year across the basin. Under projected 2050 demand scenarios, seasonal water level declines of 8 to 14 metres are modelled in heavily abstracted areas. The study recommends spatially-differentiated abstraction licensing based on the modelled sustainable yield.

Keywords: hydrogeological modelling, Sokoto Rima Basin, MODFLOW, aquifer system, sustainable yield.