Kariba Dam rehab progresses

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By BENEDICT TEMBO, Siavonga

The rehabilitation of the Kariba Dam, a transboundary infrastructure between Zambia and Zimbabwe, has reached an advanced stage.
The Kariba Dam Rehabilitation Project, funded by the African Development Bank, the European Union with counterpart funding by Zambia and Zimbabwe, has two work components – the plunge pool reshaping and the spillway refurbishment. Zambezi River Authority (ZRA) chief executive officer Munyaradzi Munodawafa said the plunge pool reshaping works are at 74 percent completion with a disbursement ratio of 75 percent.
Mr Munodawafa said this progress has seen a completion of the coffer dam, dewatering of about 36 metres depth of the plunge pool level and commencement of preparatory works for the fault zone strengthening measures.

“Todate, the project has realised several significant milestones which have gradually drawn it much closer to completion, despite the numerous challenges and setbacks that have been encountered since commencement,” he said

On a visit by a delegation from the Nile Basin Initiative (NBI) to Kariba Dam during the week, Mr Munodawafa said the expected date of completion of the plunge pool works is March next week.
“Significant progress has accrued in implementation of the spillway rehabilitation work, with key milestones achieved todate being the successful installation of the coffer dams in sluices six, three, two and one,” Mr Munodawafa said.
He said completion of civil works in sluice six, commencement of installation of the sluice two and six built in parts while manufacturing of the emergency gate and the gantry crane are ongoing in China and South Africa respectively.

“The expected date of completion of the spillway refurbishment works is February 2025,” he said

The dam, which has been in operation since 1960, has been meeting the water needs of the two power utility companies – Zesco in Zambia and ZESA in Zimbabwe – for power generation through the combined installed capacity of 2,130 megawatts following upgrades.
However, the safety of the dam faced the threat of being compromised by two major deficiencies relating to the plunge pool and the spillway.
Mr Munodawafa said the plunge pool has progressively deepened on account of the forces of the spilling water jets, particularly in the early years of its operation, as per design expectations.

He said the scouring of the plunge pool, to its current depth of about 80 metres has been accompanied by preferential erosion towards the dam foundation, which can result in catastrophic dam failure.

Mr Munodawafa said the spillway facility has also been affected by alkali aggregate reaction, a concrete swelling phenomenon which causes operational challenges for the hydro mechanical parts of the facility.
“Failure to smoothly operate the spillway facility can result in a catastrophic failure of the dam or loss of water for power generation if any gate fails to close as expected.

According to the dam break analysis study by Mott MacDonald, one of the consultants engaged by ZRA, a catastrophic failure of the dam would result in the loss of over three million lives of the downstream riparian communities.It would also contribute to significant loss in terms of economic and social aspects such as infrastructure, livestock and general livelihoods of the people both upstream and downstream of the dam, all the way to Mozambique.

And NBI executive director Sylvester Matemu said the experience sharing visit to the ZRA was a good choice given its experience of managing a 67 year old dam.

Mr Matemu was also happy to learn how ZRA was managing invasive weeds such as the water hyacinth. With some hydro power projects in the pipeline in the Nile Basin, he was happy to learn how the ZRA has been overseeing power generation in the Kariba Dam as well as the monitoring of water quality. His team was gld to hear ZRA’s resolution of historical disputes.