The Zambia government has issued an urgent appeal to the World Bank, the European Union (EU), the African Development Bank (AfDB) and other international financiers to provide funding for the rehabilitation of the Kariba dam wall, following expert confirmation that it has developed serious structural defects and warnings that it may collapse, with catastrophic results, within the next three years.

Engineers have warned that a collapse of the dam wall would put the lives and livelihoods of more than 3.5-million people in Zimbabwe, Zambia and Mozambique at risk. The dam’s guardian, the Zambezi River Authority (ZRA), has confirmed that the dam wall needs urgent rehabilitation. However, it says there is no need to panic as engineers still have the situation under control.

“While the situation at the Kariba dam wall is a cause for grave concern, the engineers on the ground have the situation under control. “This does not translate into an immediate calamity. “However, all urgency is expected in order to avert a catastrophe like failure of the dam wall [which] requires a series of rehabilitation works to avoid gradual degradation of key dam safety features, while maintaining [power generation] operations at levels acceptable in terms of inter-national standards,” says ZRA public relations manager Elizabeth Karonga.

Maintenance Programmes She adds that the authority has identified three critical dam maintenance programmes to be undertaken temporarily while a lasting solution is sought. Major structural defects include the spillway, which is no longer bending and does not open automatically, owing to the expansion of the concrete on the walls and heavy accumulations of rust on the steel bars.

Additionally, the plunge pool below the dam wall has reportedly deepened from an initial 10 m when the dam was built in 1959 to nearly 90 m – into the rock layer – at several points along the dam wall. The plunge pool erosion is reported to be gradually moving towards the 128-m-high wall, leading to fears that it may soon be undermined, destabilised and eventually collapse as the stabilising rock layer continues to erode.

Major preventive engineering works to be undertaken immediately include the reshaping and stabilisation of the dam’s plunge pool to limit scouring and erosion, which threaten to undermine the dam’s foundation and induce a collapse. The second phase will focus on the refur-bishment of the spillway and involves redesigning works, fabrication works and the installation of a new emergency spillgate.

The dam also needs a new gantry to prevent uncontrolled loss of water in the event of flood-gate failure, which engineers fear could result in water levels dropping below the minimum operational levels and lead to long-term inter-ruptions of power generation operations. The third and final phase involves the refur-bishment of the upstream stop-beam guides and total replacement of secondary concrete structures to prevent failure during the operation of stop beams.

The Zambia government says it has launched an international appeal to save the dam wall from collapse, amid reports that the capital city, Lusaka, lies in a zone of severe potential flooding should the dam collapse. Finance Minister Alexander Chikwanda told the Times of Zambia that plegdes of assistance have started pouring in, following appeals to the AfDB, the World Bank and the EU. Chikwanda is chairperson of a special emergency panel set up to raise part of the $250-million needed to fund the major rehabilitation works on the dam wall.

Estimates According to Zambian government estimates, repairs to the plunge pool would cost at least $80-million, while the spillway would require at least $120-million. A further $50-million would be required to cover operational and incidental costs during the phased rehabilitation programme.

While Zimbabwe Energy and Power Develop-ment Minister Dzikamai Mavhaire tells Engi-neering News that government is aware of problems at Kariba, he dismisses reports that the dam wall is in danger of collapse.

“We have seen those reports in the media and we believe they are based on hype which does not present the correct picture of the situation. The dam certainly needs repairs but to say some-thing needs repair is not the same as saying it is collapsing. Design Tenders “The warnings have been there from as early as 2009 and the Zimbabwe government is taking measures to ensure that our people are safe and the power generation process is not interrupted,” he says. The Kariba hydroelectric scheme generates a signification proportion of Zambia’s and Zimbabwe’s electricity

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He adds that the Zimbabwe government has finalised design tenders for the reshaping of the plunge pool, which should be completed by the end of 2017, and for the refurbishment of the spillway over six years. Both projects are set to begin in 2015.

According to the ZRA, the collapse of the Kariba dam would release 183 km3 of water from Lake Kariba and an additional 52 km3 from the downstream Cabora Basa dam, in Mozambique, to create a combined surge of 273 km3 of water, flooding in Zambia, Malawi, Mozambique and Zimbabwe.