RESEARCH ON KOKA RESERVOIR WATER LOSS PROBLEMS

ABSTRACT

The koka dam which was built for hydroelectric power source has been facing leakage problem since the completion of the dam in 1960. Previous studies regarding leakage problem in Koka Lake have concluded that leakage occurs all along the Koka lake bed sediments. The present study was proposed to check and prove the validity of the previous ideas of leakage and to identify and prove the major gross leakage ways. In order to solve the leakage problem, integrated survey which includes hydrogeological, geological, structural and geomorphological studies has been carried out. The present study revealed very high to very low permeability zones in the reservoir vicinities; and potential leakage area was identified in the north east down stream reservoir shore. Structures favoring major concentrated underflow from the lake to the adjacent aquifer/ ground water stretch have also been mapped within this zone. In general, ground water from the left bank far upstream right shore and the upstream areas is found to contribute to the lake and Awash river water, while underflow of this admixed water occurs via the north east down stream right shore aquifers and mega structures. This under flow water rejoins the Awash River in the down stream areas, possibly up to Nura Era station. This gives solution to the lake water-ground water-Awash River water interaction model.

Note: The report is available at the Central Technical Library of the ESTC.

(Report 1995)

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