Dam Synchronisation and Flood Releases - agriwaterpedia.info

DAM SYNCHRONISATION AND FLOOD RELEASES IN THE ZAMBEZI RIVER BASIN: ANNEX 4 OF FINAL REPORT
Reflection on Mphanda Nkuwa design
The Mphanda Nkuwa dam, located on the Zambezi river, downstream of Cabora Bassa dam was
the designed with a spillway consisting of 13 radial crest gates (Lahmeyer International et al.,
2003), and a discharge capacity of 31 000 m 3 /s while a 10 000 year flood at this site is 33 000
m 3 /s. The spillway capacity is therefore slightly below this extreme event. Because of the radial
crests this dam is associated with the same advantages as for Batoka Gorge in terms of
backwater effects.
The bottom outlet accommodates 2290 m 3 /s and the combined turbine outflow is 2200 m 3 /s.
This combined flow, including additional contributions downstream from tributaries, is expected
to be sufficient to provide for existing proposals to release freshets of 2900 m 3 /s annually from
Cahora Bassa (Lahmeyer International et al., 2003). Further studies will need to be carried out to
ensure that the freshet requirements can be met. Otherwise, larger bottom outlets would be
recommended.
Reflection on additional hydropower production using existing reservoirs
Investment projects on the main dams in the catchment not only imply new dams but also
additional power generating capacity making use of existing reservoirs. Extension of hydropower
capacity is planned for Kariba North (currently being built), Itezhi-Tezhi Hydroelectric Project,
Kafue Gorge Lower and Cahora Bassa Extension. Such extensions do not create extra storage
capacity for flood control, but increase the possibility to release water through turbines when
floods are forecasted and during floods. This adds considerably to hydropower production and
the possibility to lower dam levels before extreme floods.
3.4 Decision stage of investments
The proposed extensions to the current hydropower schemes have reached advanced stages in
the decision making process. Kariba North is currently being executed. A final impact
assessment is currently being done for Cahora Bassa Extension. A recent publication also
indicated that the Kafue Gorge Lower run-of-river scheme will be implemented
(www.hydropower.com August 2010).
There are no official statements of what is next in terms of plans for Batoka Gorge, but the
stakeholder views summarized in section 3.2 indicates that this will soon, or is already in, a final
decision making stage.
It was recently publicly announced in the press that Mozambique‘s government has approved the
construction of the Mphanda Nkuwa (www.hydropower.com August 2010 and signing of
concession contract December 2010). Its construction is planned to begin in 2011 and is
estimated to take five to six years.
It was also announced that Zambia has signed an agreement with two Chinese firms to build the
Kafue Lower Gorge hydropower plant (www.hydropower.com August 2010). The project is
planned to start in April 2011 and be completed in 2017.
The Boroma and Lupata dam are under pre-feasibility phase and are selected for feasibility study.
The Ministry of Energy of Mozambique announced in 2009 that a socio-economic study was to
be carried out for the construction of the Boroma dam and the feasibility study for the two sites
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