ASSESSMENT OF THE GROUNDWATER POTENTIAL ZONES USING ANALYTICAL HIERARCHY PROCESS METHOD AND VERTICAL ELECTRICAL SOUNDING TECHNIQUES: THE CASE STUDY OF BATENA – GUDER CATCHMENT, CENTRAL ETHIOPIA.

Abstract

Accurate assessment of groundwater potential zones is crucial for effective resource planning and use in complex hydrogeological systems. The main aim of this study is to use geographic information systems (GIS) based AHP and electrical resistivity techniques to identify the groundwater potential zones in the Batena - Guder Catchment (Hadiya Zone District, Lemo & Analemo Woreda). Thus, the groundwater potential of the research region has been identified by overlaying the weights of ten thematic elements, and then assigning numerical weight and ranking based on the GIS data. Availability of the groundwater in the watershed covers 690.4 km2, which is designed into five categories; “Very low”, “Low ”, “Moderate”, “High” and “Very high” Groundwater Potential zones viz., 76.27 km2 (11.05%), 166.43km2 (24.11 %), 170.98 km2(24.77 %) and 172.51 km2 (24.99 %) respectively. The “Very High” Groundwater potential covers 104.21 km2 (15.09 %). The study used Schlumberger configurations to acquire 10 Vertical Electrical Sounding (VES) with 4 profiles to determine depth, resistivity, thickness, and geoelectric sections. The data is analyzed using ZondRes2D software in three geoelectric layers. Based on the result profiles 1,2 and 4 show moderate to high groundwater potential occurrences with a low resistivity(<10 Ω.m) value. Groundwater zones are typically found in the middle layer, which is thicker than the top and has a higher porosity than the top layer. The validation of the drilling sites with groundwater potential zones was achieved through 36 shallow wells and 7 borehole logs data, resulting in a fairly satisfactory 74.5% agreement. The sensitivity analysis suggests that rainfall has the greatest impact on high and extremely high groundwater potential maps.