Reservoir Operation And Establishment Of Operation Rules For Lake Tana
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Date
2005-01
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Addis Ababa University
Abstract
Lake Tana, naturally existed reservoir, located in the northern portion of the Abbay river basin is the
largest lake in Ethiopia with an average water surface area of 3110 km2 and estimated drainage area of
15340 km2. It is fed by four major tributaries all of them rising in the highlands surrounding the Lake.
One regulation weir, Chara-Chara, is constructed at its out let to regulate the lake water for hydropower
productions from two existing plants (Tis Abbay I and II) and for the realization of the envisaged
development works both in the Tana and Beles Basins. With an estimated mean annual inflow of
12051.5MCM, water resources of the Lake is currently utilized only for hydropower generation at Tis
Abbay I & II, local transport from Gondar to Bahir Dar, largely traditional level fishing and for tourist
attractions at Tis Esat fall.
Recently conducted Abbay river irrigated master plan project studies (BCEOM and associates, 1999)
has indicated that the Tana and Beles basins all together have irrigation potential of more than
268,000ha out of which more than 145,000 ha is identified in the upstream reaches of the Lake Tana
reservoir. At times of realization of the envisaged development works, irrigation and hydropower
development works are, thus, becoming competing demands in the basin. Envisaged development works
in the Beles basin are also competing with those in the Tana basin. This situation reveals that planning
and reservoir operation in the basin is a serious issue that needs great attention, one of the principal
reasons for this research work to be thought.
Establishing the water balance of the lake on a monthly time scale is a prerequisite to effect reservoir
operation. This activity is performed applying the continuity equation. Final result of the water balance
simulation for the lake has shown that 69.2% of the inflow is lost through reservoir losses and 31% lost
as an outflow. Currently the reservoir is operated at some operation rule that satisfies the demand from
the existing hydropower plants and minimum requirements of the Tis Esat fall. Reservoir operation in
this research work is simulated based on deferent envisaged and existing development scenarios that
bear different magnitude of demands to the reservoir. Including the existing condition the research work
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Keywords
Operation ;Rules