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DAM SYNCHRONISATION AND FLOOD RELEASES IN THE ZAMBEZI RIVER BASIN: ANNEX 4 OF FINAL REPORT Investment Comment Chapter run-of-river dams can contribute to flood protection. However, their financial viability and the deficit of power in the region, may put pressure on optimal hydropower production. Bottom outlets Bottom outlets are required on all dams to decrease water levels in times of emergency and to maintain environmental flow releases. The use for scouring of sediment in large dams to supply sediment downstream should be cautiously approached, because of the following reasons: (a) flushing can have detrimental environmental impacts both in the reservoir and downstream; (b) flushing implies emptying the reservoirs at the beginning of the flood season, which is only an option for small and medium sized dams that do not generate hydropower; (c) for large reservoirs flushing is not an option as sediment has already settled upstream. For environmental flow releases, also the operation of the bottom outlets should be done with care, as often mixing with water from the top of the reservoir is necessary to prevent downstream water quality problems. Flood risk zoning A staged approach is recommended to coordinate flood hazard mapping, which can serve for warning and rescue, for informing new developments and for awareness raising. Floodprone zones mapping is not urgent in most areas, as local floodrisks are known. Flood risk zoning for insurance purposes is not considered feasible. 10.4 Promising investments The investments below are recommended to be supported by ZAMCOM / SADC. Table 10.4: Promising investments Investment Comment Chapter Improved flow forecasting system coupled with dispatching Centre SAPP Extra hydropower generation on existing dams An integrated forecasting system is indicated by different stakeholders as top priority and further explained in Annex 3. It will also contribute to optimization of power production. Extra turbines on existing dams will not only contribute to power generation, but will also increase the capacity to generate hydropower if reservoir water levels are to be reduced before forecasted floods, as more water is able to pass Intervention Sheet 9 4.5 7 4.6 Annex 3 + Ch. 9 Intervention Sheet 4.10 4 4.2 98
DAM SYNCHRONISATION AND FLOOD RELEASES IN THE ZAMBEZI RIVER BASIN: ANNEX 4 OF FINAL REPORT Investment Comment Chapter Electricity interconnector Malawi and Mozambique New interconnectors in SAPP Small and medium dams on tributaries Extra spillway for Cahora Bassa Elevated schools and public buildings through the turbines rather than spillways. Such projects are planned for Kariba North, Itezhi-Tezhi Hydroelectric Project and Cahora Bassa Extension. While evaluating the water management options for the Shire, it became clear that the high dependency of Malawi on power of the Shire decreases possibilities for water management. The Interconnector Malawi- Mozambique would make it possible for Malawi to obtain power from SAPP, creating less stress on the Shire River. When new interconnectors are established, the SAPP countries will have less blackouts and the countries with a surplus of hydropower (during certain periods of the year) have more possibilities to export their electricity production. Different stakeholders indicated that for the Zambezi region creating possibilities for livelihoods on tributaries has less negative environmental impacts and is contributing to the economy. The flood protection impacts are limited, but the contribution to livelihoods may create alternative locations for resettlements of persons currently living in floodprone areas. The extra spillway is very beneficial for the ecosystem upstream and downstream of Cahora Bassa Dam. However, the impact on the maximum floods still has to be studied further together with the flood operation rule curves considered. A hydrological study has been planned by HCB. Combining the advantage for improved public buildings such as schools with the need for refuge areas in terms of floods is a win-win situation that is promising. In the Limpopo river basin good examples have been built. Intervention Sheet 4 4.9 11 4.9 5 4.3 6 4.4 8 4.7 99
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