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.