GROUNDWATER RESOURCE ASSESSMENT IN HARD ROCK TERRAIN USING CONVENTIONAL, REMOTE SENSING AND GIS APPROACH IN SOUTHERN PERIPHERAL PART OF ETHIOPIA

Integrated studies were implemented for studying the groundwater resource in the drought prone peripheral part of Ethiopia, Negelle Borena. Analysis of hydrometeorological components shows that mean precipitation for the catchment is about 647mm per annum. Actual evapotranspiration is evaluated using the simple “book keeping” Thornwait and Mather method and is found to be about 93.6% of the annual input from the precipitation. The mean annual recharge to the catchment is 31.4mm and about 9.2mm of water leaves the catchment as surface runoff. Five hydrostratigraphic units have been characterized based on porosity, permeability and storage capacity. Recharge area in the catchment is mainly confined to the Phanerozoic cover and the discharge areas are in the basement terrain. Application of the GIS and remote sensing shows that movement of groundwater in the study area is mainly controlled by structures. A series of water types was identified in the study area, hydrochemical studies reveal that the hand dug wells mainly on the basement show variety of water types calcium-bicarbonate, calcium-chloride-bicarbonate and calcium-sodium-chloride-bicarbonate attributed to the arid condition of the area. The intersection on other lineament orientations and the NE-SW structures are considered to be the potential sources due to the effect of double porosity, the NE-SW structures existing at topographically depressed (south western) parts of the study area are also considered to be potential sites, which is in agreement with the available ground data.