Groundwater Potential Mapping in Crystalline Basement Terrain Using an Integrated Geophysical–GIS Approach: Mubi, Northeastern Nigeria

Abstract : Groundwater is the primary source of water supply for domestic and agricultural purposes in Mubi and environs, northeastern Nigeria. This study integrates geological field mapping, vertical electrical sounding (VES), and hydrogeophysical parameter estimation to delineate groundwater potential zones within an area of approximately 216 km² (longitudes 13°12′00″ E – 13°20′00″ E; latitudes 10°12′00″ N – 10°20′00″ N). Detailed geological mapping reveals that the study area is underlain predominantly by porphyritic granite and fine-grained granite, with eluvial deposits occurring in the southwestern and southeastern portions. A total of 40 VES stations were surveyed using the Schlumberger electrode configuration, and data were interpreted using INTERPEX resistivity software. Quantitative interpretation identified four curve types: H (62%), KH (15%), A (10%), and QH (13%), indicating weathered and fractured/weathered aquifer systems. Aquifer characterization using Dar Zarrouk parameters shows that transverse resistance ranges from 12.38 Ω·m² to 5029.51 Ω·m² (mean: 1347.03 Ω·m²), while longitudinal conductance ranges from 0.01 Ω⁻¹ to 4.51 Ω⁻¹ (mean: 0.69 Ω⁻¹). Based on longitudinal conductance, the aquifer protective capacity is classified as poor (5% of VES points), weak (12.5%), moderate (47.5%), and good (35%). Transmissivity values range from 5.89 m²·d⁻¹ to 748.78 m²·d⁻¹ (mean: 333.01 m²·d⁻¹). Aquifer potential rating based on transmissivity indicates moderate potential in 77.5% of the area, high potential in 17.5%, and low potential in 5%. Integration of these results with a GIS-based analytical hierarchy process using seven thematic layers (geology, land use/land cover, soil, rainfall, lineament density, drainage density, and slope) produced a groundwater potential map classifying the area into poor, moderate, and good potential zones. The consistency ratio of 0.0049 confirms the reliability of the analytical hierarchy process weighting. This study demonstrates that combining conventional geoelectrical methods with GIS-based multi-criteria decision analysis provides a robust framework for groundwater resource evaluation in crystalline basement terrains.  Keywords: Porphyritic granite; Vertical electrical sounding; Dar Zarrouk parameters; Aquifer transmissivity; Groundwater potential; Mubi; Nigeria