GROUNDWATER POTENTIAL ASSESSMENT USING INTEGRATED ELECTRICAL RESISTIVITY AND MAGNETIC METHODS : A CASE OF ENTO CATCHMENT, BODJI DIRMEJJI DISTRICT,OROMIA, ETHIOPIA

Major Advisor: Dr. Geremew Lemessa This study was conducted in the Ento watershed region, Bodji Dirmejji district, Oromia,<br> Ethiopia. Water supply has been a problem in the study area. There is now only one<br> existing borehole. The yield of the water is 200 m³ per day (200,000 liters per day), but<br> the population of the town is 22,000 (twenty-two thousand). To close this gap, assess<br> groundwater potential using integrated electrical resistivity and magnetic methods to find<br> out the location of preferred borehole areas and the depth at which the aquifers are<br> located. Data were acquired from fifteen VES points using the Schlumberger electrode<br> array, with a maximum half-current electrode spacing of AB/2 = 330 meters, along with<br> 155 magnetic data points. The VES and magnetic datasets were processed using IP2WIN,<br> IPI2Win-Res3, Surfer 10 (32-bit), and Oasis Montaj 6.4.2 software.The interpretation of<br> VES data was carried out using resistivity curves, geo-electric sections, and pseudosection<br> maps. Similarly, magnetic data interpretation involved several anomaly maps,<br> including total magnetic field, residual magnetic field, analytical signal, and upward<br> continuation maps. Field results from the VES survey revealed zones of low resistivity,<br> suggesting potential groundwater presence. Along Profile 1, VES 3 and VES 4 show a<br> third layer with a thickness of 35 m, resistivity ranging from 76–98 Ωm, and extending to<br> a depth of 51 m. This continues into a fourth layer at VES 4, which is 38 m thick, has a<br> resistivity of 142 Ωm, and reaches a depth of 89 m—indicating favorable aquifer<br> conditions. At VES 8, the third layer is 31 m thick with a resistivity of 61 Ωm and extends<br> to 49 m, while the fourth layer is 38 m thick, has a resistivity of 119 Ωm, and reaches a<br> depth of 87 m—also suggesting aquifer potential. Similarly, the third layer at VES 15,<br> with a thickness of 48 m, resistivity of 62 Ωm, and depth of 62 m, is identified as a<br> promising aquifer zone. Meanwhile, the magnetic survey results revealed low magnetic<br> anomalies in the southwest to northwest regions of the study area, particularly in the<br> upward continuation maps. These low magnetic responses suggest areas of intense<br> weathering and fracturing, likely due to weakened geological structures. The integrated<br> interpretation of VES and magnetic data, along with geological information, provided a<br> comprehensive understanding of the subsurface conditions.<br> Key words: Ento watershed, electrical resistivity, magnetic methods, groundwater,<br> Resistivity Curves, geo-electric section, and residual magnetic field map.