Tandem Reservoir Operation of Cascade Hydropower Plants Case of Genale - Dawa River Basin
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Date
2014-09
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Addis Ababa University
Abstract
Genale – Dawa river basin is one of the twelve river basins in Ethiopia with catchment area
of 74,010 Km2 and has the third largest surface area (about 170,000km2) after Wabishebele
and Abay River basins. Genale-Dawa river basin has an estimated hydropower potential of
9,300 GWh/year and is expected to contribute about 5.8% of the total estimated potential of
the country.
Out of the nine large scale hydropower potential projects in the basin, this study deals with
the optimal operation of the cascade hydropower plants namely, GD-3, GD-5 and GD-6 that
are located on the main river channel of Genale River. The upper most hydropower plant,
GD-3, is already under construction and the other two are under study.
The latest version of HEC-ResSim (Version 3.1) introduced by U.S. Army Corps of
Engineers in 2013 is used to simulate the multi-reservoir system network. The physical and
operational data are obtained from previous studies of these projects and used as input in
reservoir network module of ResSim Model. Implicit (default) and Explicit (user defined)
system storage balance has been used to get the maximum power and energy and plot the
optimal guide curve so as to be used by the operator to attain the optimal overall energy
generated from the system. The explicit system storage balance has generated a better power
and energy for the reservoir system.
The study showed that, when the individual hydropower reservoirs deliver energy and
capacity into a common power system, operating the projects as system has produce more
average energy or firm energy than the sum of individual projects operating independently.
The maximum overall average energy of the system found in this study is 4417.7GWh/yr.
Comparing with the feasibility study, the proposed model is capable to produce an extra
amount of 487.7 GWh average electrical energy (a 12.4% increment) annually.
The optimal guide curve denotes that there is a tendency, in the optimal explicit system
storage, to leave more water from GD-3 reservoir and prepare the storage to hold more water
during high flood seasons. The water released from this reservoir can generate additional
power at the downstream power plants. The reverse is true for the operation of the
downstream power plants. The pool level of GD-5 is almost in the flood zone except for the
first three months, January to March, where the pool level is in the active live storage zone. In
GD-6 the reservoir pool level is in the flood zone throughout the year.
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Dawa River Basin