Groundwater potential assessment using electrical resistivity tomography and magnetic methods: a case of ganja catchment, west wallaga zone, gimbi area

ABSTRACT

Gimbi Town in the West Wallaga Zone of the Oromia Region, Ethiopia, is facing growing pressure on its water resources due to rapid population growth, expanding agriculture, and an unreliable surface water supply. According to the World Health Organization (WHO), Ethiopia is classified as a developing country where access to sufficient water remains a major challenge. In Gimbi Town, the daily water supply from surface reservoirs falls significantly short of meeting the population's needs, resulting in a substantial deficit compared to WHO's recommended per capita water consumption. This water shortage has serious implications for public health, economic activity, and community well-being. To address this, the study assesses the groundwater potential of the Ganja Catchment using integrated geophysical techniques—Electrical Resistivity Tomography and magnetic survey. The main objective is to evaluate groundwater potential, with specific goals of mapping subsurface resistivity, identifying aquifer-bearing zones, detecting geological structures, and targeting highly fractured and weathered rock formations. ERT data collected along five profiles using the Wenner array and processed with RES2DINV revealed three resistivity zones: low resistivity 38.8–90.6 Ωm in weathered and fractured materials with high groundwater potential; moderate resistivity 121–138 Ωm in partially weathered transition zones with moderate yield; and high resistivity 323–754 Ωm in compact bedrock with minimal potential. Productive aquifers are mainly located in the weathered and fractured schist and gneiss formations. Magnetic data, collected along five traverses and processed in Oasis Montaj, showed low magnetic anomalies −6.245 to 2.821 nT in the southern region, indicating weathered, porous zones ideal for groundwater storage. Transitional anomalies 3.502 to 9.117 nT in the central eastern area reflect mixed lithology with moderate potential, while high anomalies 9.725 to 25.087 nT in the central, northern, and western parts correlate with compact rocks (gneiss, amphibolite) of low potential. The integrated ERT and magnetic survey results confirm that the southern and northeastern parts of the Ganja Catchment have the highest groundwater potential. Transitional zones offer moderate potential, while compact zones show minimal potential. These findings provide a reliable geophysical basis for effective well placement and groundwater resource planning.

Keywords: Groundwater potential, ERT, Magnetic survey, Ganja Catchment, Aquifer zone