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Kariba Dam rehab underway, won’t affect electricity supply

THE arch dam which was constructed between 1956 and 1959 supplies water to two underground hydropower plants located on the north bank in Zambia and on the south bank in Zimbabwe.

AFTER more than 50 years of providing power for the southern African region, the Kariba Dam is now in urgent need of rehabilitation to ensure it continues to operate safely. A program of civil works conducted over the next ten years has been prepared, taking into account the need to continue operating the dam safely with minimal interruptions of power generation. Specifically, the rehabilitation works will include the reshaping of the dam’s plunge pool and refurbishment of its spillway, as well as making improvements in dam operations.
Our staffer TEDDY KUYELA, was in Siavonga to attend a public discussion organised by Zambia Environmental Management Authority (ZEMA) on the status of the Kariba Dam now reports.
The Kariba Dam is a double curvature concrete arch dam located in the Kariba Gorge of the Zambezi River basin between Zambia and Zimbabwe.
The arch dam which was constructed between 1956 and 1959 and supplies water to two underground hydro-power plants located on the north bank in Zambia and on the south bank in Zimbabwe, is central to regional energy security and economic development.
Water is released from the reservoir through six sluice gates. In the first 20 years after the dam was constructed there were sustained heavy spillage episodes resulting in erosion of the bedrock to 80 metres below the normal water level.
This has resulted in instability of the plunge pool making the dam wall unstable and unsafe. Moreover, the six sluice gates that make up the spillway have been damaged by advanced alkali silica reaction to the concrete.
The Zambezi River Authority (ZRA), the bi-national organisation that manages the dam on behalf of Zambia and Zimbabwe will be responsible for implementing the rehabilitation project.
The international financing made available for the rehabilitation exercise include US$75m in grants and loans from the Africa Development Bank (AfDB), a US$100 million grant from the European Union, a grant of US$25 million from the Swedish government, and a credit of US$75 million from the World Bank.
The ZRA has initiated the rehabilitation of the dam, which will see the plunge pool and the spill way worked on to allow for safe operation of the dam and prevent a catastrophic dam failure in the future. Such failure, if it were to occur, would result in a major loss of life of about three million people.
In addition to human fatality risks, dam failure would result in significant downstream environmental damage and a loss of a main source of power to the southern African region. Urgent rehabilitation is intended to prevent further degradation of dam.
In light of the above, ZRA has proposed to improve the stability of the plunge pool through reshaping its profile. This will limit the preferential erosion towards the foundations of the dam wall along zones of weak rock and allow for the safe operation of the dam and continued generation of electricity from the hydro-power plants.
The second objective of the project is to rehabilitate the six sluice gates of the spillway, enabling the ongoing use of the spillway function to safely manage the water levels in the reservoir.
Speaking during the public meeting held in Siavonga last week, ZRA Project manager Sithembinkosi Mhlanga said the rehabilitation and re-construction of the dam will take approximately nine years but will not affect the provision of electricity in both countries.
Mr Mhlanga said the dam will be rehabilitated in two phases starting with the plunge pool which is about 80 metres by putting another strong foundation layer which will take about three years to be completed then coming to the six spillway gates which will also take approximately six years.
He assured both residents of Zambia and Zimbabwe not to panic because there will be no interruption of electricity supply during the rehabilitation exercise.
“We are grateful to our development partners for their cooperation in mobilising financial support. Kariba Dam is an important regional asset that affects the lives not only of Zambian and Zimbabwean citizens, but those of the citizens of the countries in the Zambezi river basin, as well as of countries connected to the Southern Africa Power Pool,” Mr Mhlanga said.
ZRA director responsible for water resources and management Christopher Chisense said the project will be done by supporting the reshaping of the plunge pool, refurbishment of the spillway gates and enhancing operations to bring them in line with international dam safety standards.
ZRA has finally submitted an environmental impact assessment report to ZEMA for the repair of the plunge pool and the spillway at Kariba Dam.
ZRA was formed by the Zambezi River Authority Act of 1987 (Act No. 17 and 19 Zambia and Zimbabwe respectively and is governed by a Council of Ministers consisting of four members: two Ministers from Zambia and another two from Zimbabwe. The Ministers are those holding portfolios of Energy and Finance in the respective countries.
The functions of ZRA include operating, monitoring and maintaining the Kariba complex, all telemetering stations relating to the Kariba Dam and any other installations owned by the Authority.
As part of the proposed rehabilitation project, ZRA has committed to comply with international guidelines and standards, and as such it is required to undertake a full Environmental and Social Impact Assessment (ESIA) for the Project.
In accordance with the Zambian and Zimbabwean Environmental Management Acts, there is a legal requirement for the project managers to respectively submit an Environmental Scoping Report and an Environmental Prospectus report as part of the overall ESIA process.
As per the agreed outcomes in a meeting held with the Zambian and Zimbabwean Environmental Management Authorities on November 24, 2014, held at ZRA administrative block in Kariba, in which the implementation of a harmonised ESIA process was discussed, a joint Scoping/prospect report was submitted to both Environmental Authorities for review.
This prospectus report fulfilled the Zambian requirements for a scoping report and Zimbabwean requirements for a prospectus report, and has since been approved by ZEMA.

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