Dam Synchronisation and Flood Releases - agriwaterpedia.info

DAM SYNCHRONISATION AND FLOOD RELEASES IN THE ZAMBEZI RIVER BASIN: ANNEX 4 OF FINAL REPORT
9 Diversification of the Electric Power Pool – Thermal and
Hydropower Plants
9.1 Introduction to the investments
During the wet season, tributaries downstream of a major dam may be discharging large volumes
of water into the main river. In such situations, the release of dam water for hydropower
generation increases risk of flooding downstream of the tributary and is unwelcome. The units of
power generation could be taken out of service to the extent that such action will not contribute
to flooding upstream of the power plant and the damage of stopping power generation is
acceptable. Thermal power plants could help in generating additional energy at such times when
hydropower turbines are need to be shut, to keep flows downstream to a minimum.
Figure 9.1 is a schematic illustration of the above processes. If the tributary peak flow (y) is far
larger than the maximum turbine flow (x) then shutting down of the turbines will not contribute
to flood protection.
This Chapter discusses possible alternate energy options in order that hydropower plants can be
considered for use in flood control.
When good meteorological forecasting systems are available, hydropower plant operators can
match their power production with optimal control of the dams. In this manner they have better
control of reservoirs and river flows downstream. To combine flow forecasting with power
generation coordination is an investment option which is also discussed in this chapter.
Tributary River
Tributary causing potential flooding
Peak flow
(Y m 3 /s)
Upstream
P Plant
Flow of water
Possible
Flood
risk
Max turbine flow
(X m 3 /s)
Downstream
Figure 9.1: Conceptual diagram showing control of flooding contribution using hydropower plants.
9.2 Situation Assessment: expert views
In the process of replacing hydropower plants with thermal power, the criterion that is mostly
used is m³/MWh. This coefficient relates to the water that is used to produce energy. It is used
to reflect the amount of energy to be substituted for any volume of water that will not pass
through the turbine. As an example, for the North extension of Kariba Dam, the flow through
each turbine of 180 MW is about 230 m 3 /s. This means that for every MWh needed, 4600 m 3 of
water will be used.
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