Hydrogeological And Hydrogeochemical Assessment In The Adama (nazareth)-dera Area Centeral Ethiopia

The investigated area, Nazareth-Dare sub-casement is located in the central part of the MainrnEthiopian Rift within 80 09’24.58’’ to 80 36’28.75’’N latitude and 390 08’36.70’’to 390rn27’47.23’’E longitude and covers about 941 km2. This research work assesses thernhydro geological and hydroelectrically nature of the area based on the analysis of hydrornpetrology, hydrology, hydro geology and hydro geochemistry data. The assessment andrninterpretation of the chemical analysis of the previous works and the current works are made tornaccomplish this objective.rnThe area has semi-arid to semi-humid climate with a mean annual temperature and precipitationrnof 21.470C and 807mm respectively. The study area has both flat and rugged topography. Thernannual potential transpiration and actual transpiration of the area are calculated to bern1979.1mm and 726.55mm respectively.rnThe total annual estimated runoff value that leaves the casement area is to be 175.72MCM. Inrnthe study area the direct groundwater recharge from precipitation is negligible. Instead, there isrnhuge amount of groundwater recharge from Koka Lake, which is inflow for the study area to bern485.4 MCM/annum. Values of net annual groundwater recharge estimate is determined fromrnwater balance calculation and found to be 298.36 MCM.rnConcerning the hydro ornithological characteristics of the area, there are four hydro ornithologicalrnunits which are grouped as high to very high, Moderate to high, low to moderate and low to veryrnlow permeability groups. The main aquifer units in the area are alluvial, volcano- clarinetistrndeposits, weathered and fractured basalt and ignites, which have generally greater thanrn2m/day permeability whereas, all fresh basaltic flows and domes, holistic and trachea rockrnunits and pumice and ash fall deposits, densely welded fine-grained and green ignites havernpoor permeability.rnAccording to major ions hydro geochemistry analysis result and tree-linear piper diagram plotsrnmost of the borehole waters are Na-HCO3 and Na-Ca-HCO3 type, springs and all hand dug wellsrnare Na-HCO3 water type. All Awash River samples in the area are Na-Ca-HCO3 water type.rnBased on the analysis results of major cations and anions, the general water quality are discussedrnfrom public supplies, irrigation and industry point of view. Concerning the water quality, Wonjirnand Sod ere area have groundwater with ionic concentration of Na, TDS and fluoride beyondrnpermissible limit.rnConcerning water pollution, the underlying unconfined shallow aquifers groundwater in Wonjirnarea and alluvial aquifers along Awash River may be generally considered as highly vulnerable to and type of pollution.

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