Hydrogeology of Debre Zeit Area

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Addis Ababa Universty


The investigated area is located east of Addis Ababa on the western border of the main Ethiopian rift valley * Being part of the Ethiopian rift system , it is characterized by Plio-Quaternary volcanism which gave rise to trachytic- domes, rhyolitic flows , and rhyolitic ignimbrites in the highly elevated part of the area while olivine basaltic flows and surge deposits in the lower elevated plain area . The maximum point in the area is represented by Mt . Yerer with an elevation of 3100 m above sea level. The plain area has an average elevation of 1900 m above sea level . The yearly minimum possible rainfall average in the area is 859.9 mm , the actual and potential evapotranspiration is 606 , 2 and 857.1 mm respectivly and the runoff that leaves the basinis 25 . 568 x 10d m3 «of water. From these determinations, the amount of infiltrated water in the area is <5 3 calculated and the value is 54.39 x 10 m . The hydraulic parameters , transmissivity and hydraulic conductivity are determined based on the pumping test information obtained for few wells , The transmissivity and permeability of the rocks found in the central part “3 2 \ _3 of the area is 0 ,9x10 m /s and 4.0-5x 10 cm/s respectively .8 ,8 x 10 m and the latter is 1.5 x 10 cm/s. But the storage coefficient is not calculated because of the absence of observation wells in which the effect of further drowdown is observed , Because of the lack of bore wells in the northern part, of the area , a thorough study of the actual variation of groundwater level was not possilble. But based on the available static level data , for the central part of the area , appropriate groundwater level contour lines are constructed The chemical analyses result- showed that most waters are calcium -magnesium-bicarbonate type .



Debre Zeit Area