Establishing Water Release Rules for Koka Reservoir for Wet Seasons.
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Date
1998-12
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Addis Ababa University
Abstract
Koka is the only single Reservoir found in the Upper Awash River Basin being utilised
both for Hydropower and Irrigation uses. The current maximum capacity of the reservoir is
estimated at 1,000 million rrr'. Up to the inlet to the Reservoir, the Upper Awash River Basin
drains a catchment area close to 11,300 Km2. A number of important schemes found at the
flood prone areas, downstream of the reservoir, are in need of a workable operation rule for
Koka which can give them some protection against flooding during wet seasons.
In this research an operation rule curve is established. The operation rule curve is
established in such a way that all important variables for the hydropower operation and flood
control are optimised subject to the constraints. Linear programming in MS-FORTRAN
language is used to develop the optimisation model for Koka reservoir operation. The dry
season water requirements of downstream irrigation schemes are implicitly guaranteed since
the optimised rule curve will ultimately lead to a full storage at the end of every wet season
which is desirable by those schemes.
Emphasis was also given on the flexibility of the model to allow adaptive operation
rules responding to the changing constraints and boundary conditions which are quite
noticeable in the Koka reservoir system. The Real-Time operation procedure is formulated to
be used in conjunction with the established rule-curve to enable the reservoir operators to
make decisions, regarding releases for various purposes, in a considerably shorter period of
time (e.g.,daily) using the current hydrometeorological information.
The most important component in Real-Time reservoir operation is the Rainfall-Runoff
model. These models enables, for a known rainfall, to predict the expected runoff which is an
important information for the Real-Time operation of the reservoir and for assessing the
possibility of flood hazards well in advance of its catastrophic consequences. It is, however,
unfortunate that most models are data intensive that the scarcity of data is the major bottleneck
in using them. In this research, a rainfall-runoff model is established employing the SCS
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Keywords
Koka ;Reservoir