Three-dimensional electrical resistivity tomography for groundwater mapping in the Abéché Basin, Chad

Groundwater resources in semi-arid crystalline bedrock regions are essential, yet challenging to locate due to pronounced subsurface heterogeneity. In the Abéché Basin (Chad), traditional prospecting methods achieve low drilling success rates (~ 40%). This study demonstrates the effectiveness of an integrated 2D and 3D Electrical Resistivity Tomography (ERT) approach for improving groundwater exploration in this urban Sahelian setting. We acquired 20 two-dimensional (2D) profiles and seven three-dimensional (3D) survey blocks across ten neighborhoods. Validation against eight boreholes confirmed a success rate of 75% (yield > 1 m3/h), significantly outperforming traditional methods. A significant negative correlation was established between bulk resistivity and yield. ERT identified low-resistivity anomalies (< 200 Ω·m) associated with fractured zones proximal to temporary watercourses, delineating preferential recharge pathways. This work provides a validated, replicable framework that positions 3D ERT as a robust tool for sustainable groundwater mapping in complex crystalline aquifers, directly supporting water security goals in Sahelian urban areas.