Hydrogeological and Hydrogeochemical Assessment in the Adama (Nazareth)-Dera Area, Centeral Ethiopia

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Addis Ababa University


The investigated area, Nazareth-Dare sub-casement is located in the central part of the Main Ethiopian Rift within 80 09’24.58’’ to 80 36’28.75’’N latitude and 390 08’36.70’’to 390 27’47.23’’E longitude and covers about 941 km2. This research work assesses the hydro geological and hydroelectrically nature of the area based on the analysis of hydro petrology, hydrology, hydro geology and hydro geochemistry data. The assessment and interpretation of the chemical analysis of the previous works and the current works are made to accomplish this objective. The area has semi-arid to semi-humid climate with a mean annual temperature and precipitation of 21.470C and 807mm respectively. The study area has both flat and rugged topography. The annual potential transpiration and actual transpiration of the area are calculated to be 1979.1mm and 726.55mm respectively. The total annual estimated runoff value that leaves the casement area is to be 175.72MCM. In the study area the direct groundwater recharge from precipitation is negligible. Instead, there is huge amount of groundwater recharge from Koka Lake, which is inflow for the study area to be 485.4 MCM/annum. Values of net annual groundwater recharge estimate is determined from water balance calculation and found to be 298.36 MCM. Concerning the hydro ornithological characteristics of the area, there are four hydro ornithological units which are grouped as high to very high, Moderate to high, low to moderate and low to very low permeability groups. The main aquifer units in the area are alluvial, volcano- clarinetist deposits, weathered and fractured basalt and ignites, which have generally greater than 2m/day permeability whereas, all fresh basaltic flows and domes, holistic and trachea rock units and pumice and ash fall deposits, densely welded fine-grained and green ignites have poor permeability. According to major ions hydro geochemistry analysis result and tree-linear piper diagram plots most of the borehole waters are Na-HCO3 and Na-Ca-HCO3 type, springs and all hand dug wells are Na-HCO3 water type. All Awash River samples in the area are Na-Ca-HCO3 water type. Based on the analysis results of major cations and anions, the general water quality are discussed from public supplies, irrigation and industry point of view. Concerning the water quality, Wonji and Sod ere area have groundwater with ionic concentration of Na, TDS and fluoride beyond permissible limit. Concerning water pollution, the underlying unconfined shallow aquifers groundwater in Wonji area and alluvial aquifers along Awash River may be generally considered as highly vulnerable to and type of pollution.