NVESTIGATION OF GROUNDWATER POTENTIAL USING VERTICAL ELECTRICAL RESISTIVITY METHOD:A CASE OF RIBB CATCHEMENT, SOUTH GONDAR, AND NOTRH WESTERN ETHIOPIA

Abstract

Geophysical investigation using Vertical Electrical Sounding (VES) method was conducted to investigate groundwater potential zone for Debre Tabor town at Ribb catchment and South Gondar Zone, North Ethiopia. The main objective of this study was to investigate Groundwater potential using vertical electrical resistivity method at Ribb catchment for Debre Tabor town.The aquifer system of the catchment is multi-layer aquifer as observed from the interpreted conducted VES points. Hydrogeological site delineation carried out and then geophysical investigation conducted specifically Vertical Electrical Sounding (VES) method. The data acquired from sixteen (16) VES points using Schlumberger electrode arrays with maximum half current electrode spacing (AB/2=500m). The qualitative analysis of VES data was carried out by using pseudo depth sections and different Geoelectrical sections. The quantitative interpretations of the Vertical Electrical Sounding data were conducted by modeling the Vertical Electrical Sounding data using Ipi2win software and constructing geoelectric sections along selected survey lines, using the result from individual Vertical Electrical Sounding point interpretations. The Vertical Electrical Sounding results of the data revealed three main geoelectric layers which differ in degree of weathering, fracturing, composition and depth of burial. The geo-electric sections enabled to identify the overburden thickness and the depth to the aquifer along survey lines. Moreover, the vertical electrical sounding survey helped to identify groundwater potential areas and determine the depth to the aquifer. The study area is probably covered by volcanic rocks with different degree of weathering and fracturing. From acidic volcanic rocks Tuff, and pyroclastic deposit are the major unit northeast and southeast direction from Debre Tabor town. Trachyte plug and flow are outcropped along ribb river catchment. Whereas from basic volcanic unit, Aphanite basalt, plagioclase basalt, scoracious basalt and scoria are the main rock exposure in the study area. Alluvial deposit is outcropped and mapped along ribb river catchment and the banks of other tributaries. It is suggested that the apparent resistivity pseudo-depth sections and the true resistivity geoelectric sections show the presence of shallow as well as deeper low resistivity horizons which are potential zones of groundwater saturation.