Water balance evaluation, leakage rate and total water loss of Koka Reservoir, Ethiopia: comments on previous studies and new determinations

Abstract

Water balance evaluation of Koka Reservoir was attempted by different authors, and different leakage rates were estimated. However, the water balance equation that the previous authors used does not take into account ground water inflow into the reservoir. Koka Reservoir is known to receive groundwater inflow from the north, west and south shores and from the reservoir floor, and loses water by leakage at the northeast reservoir bank and where it abuts on the Koka Dam. Hence, previous estimated leakage rates and total reservoir water loss are incorrect. An appropriate water balance equation is proposed for Koka Reservoir, and subsurface outflow (leakage rate) of 485 mm3/year and total reservoir water loss of 546 mm3/year are determined. The new determinations are recommended to be used for Awash River simulation model.


Key words/phrases: Ethiopia, Koka Reservoir water loss, leakage rate, subsurface inflow, water balance


SINET: Ethiopian Journal of Science Vol.25(1) 2002: 141-150