ASSESSMENT OF GROUNDWATER POTENTIAL ZONES: THE CASE OF WOGAYI WATERSHED IN THE OMO-GIBE RIVER BASIN, ETHIOPIA

Abstract

This study was aimed at assessing the groundwater potential of Wegayi watershed in the Omo Gibe river basin. Secondary data: climate, topography, well log information and different thematic layers were used. The thematic layers considered in this study are geology, geomorphology, drainage density, lineament density, rainfall, soil types, slope and land use/cover. Arc GIS and Surfer 20 softwares were used to produce spatial maps of the different thematic layers and water table contours respectively. The geological formation of the catchment was evaluated using existing well logs data of the boreholes. The groundwater flow direction of the catchment was identified by using ground water level maps. The Saaty analytical hierarchy process (AHP) method was implemented to identify the groundwater potential zones based on their relative assigned weights. Eventually, the weights were normalized so as to indicating on their importance in groundwater occurrence. The major lithological units of the area are weathered and fractured basalts. These types of geological formation are recognized to be good groundwater formations. According to the groundwater flow lines and the ground water contour maps produced in the catchment, the groundwater flows from southern and eastern parts of the highlands of the catchment towards the plain areas of the northwestern parts of the catchment. The hydraulic characteristics are variable throughout the catchment. According to the result of groundwater potential map, the major recharge of groundwater occurs in the Easter and southwestern highlands of the catchment, which is said to be recharging zone. However, the area situated in the southeastern, northwestern and northeastern parts of the catchment is discharge zones. The results of AHP indicate that 58.12% moderate, 20.82% high, 21.03% low and 0.032% very low groundwater potential zones have been identified. Finally, it is concluded that the integrated GIS and remote sensing techniques are very efficient and useful for the identification of groundwater potential zones