On Sept. 18 the Zimbabwean and Zambian governments signed agreements for US$294 million with the European Union (EU), the World Bank, the African Development Bank and the Swedish government to finance emergency dam repairs at 1,830-MW Kariba hydroelectric facility, according to the World Bank.
Since it’s commissioning in 1960, “the water was only 10-meters-deep [33 ft] at the foot of Kariba Dam, but erosion of this plunge pool has increased the depth to 90 m [295 ft] and has been wearing away rock near the dam’s foundations,” according to “Impact of the Failure of the Kariba Dam,” a report released by the Institute of Risk Management (IRM) of South Africa.
Located on the Zambezi River about 260 miles downstream of Victoria Falls in southern Africa, the Zambezi River Authority (ZRA) operates the project. IRM, along with the EU, said repairs are urgently needed.
“It was considered an emergency and the EU decided to mobilize funds as it was important to start the rehabilitation as soon as possible,” said Philipe Van Damme, the EU ambassador to Zimbabwe.
Kariba Dam, at a height of 397 ft (128 m) and a crest-length of 2,024 ft (617 m), impounds Lake Kariba, the world’s largest manmade reservoir. The Kariba hydroelectric project has been central to regional energy security and economic development, the report said.
Repair and rehabilitation will include the following:
• Reshaping the Kariba Dam plunge pool to limit scouring and erosion that could potentially undermine the dam’s foundations; and
• Refurbishing the spillway and associated infrastructure to improve the dam’s stability and operations.
The report IRM released earlier this year warns that 181 billion cubic meters of water from the facility’s reservoir would careen downstream if the dam fails. During a period of 8 to 10 hours until the flow dissipates, the report posits a wall of water would hit and likely destroy the dam at the 2,075-MW Cahora Bassa hydroelectric project downstream in Central Mozambique.
Published reports indicate Technical Director of Hidroelectrica de Cahora Bassa (HCB), the company that operates Cahora Bassa Dam, Moises Machava, said HCB has been aware of the risk to Kariba Dam.
According to Machava, the latest information is that the risk exists, but is not imminent. “It won’t happen tomorrow, or next year,” he said. “But if nothing is done, then it will happen, but not for another couple of years at least.”
The repairs could take up to a decade to complete, according to Charity Mwansa, ZRA chairperson. “Reshaping of the plunge pool will take three years, while the rehabilitation of the spillway gates will take six years with minimal disruptions to normal operations.”
Machava said HCB does not know when these repairs will begin, but given the urgency of the situation, he expected that date to be later this year or in early 2016. HCB expects to be briefed on this at the next meeting of the dam operators in early December.
Local news outlets report Machava said Lake Kariba’s volume is currently 20% lower than normal. ZRA told HCB it is keeping Kariba’s floodgates closed and does not intend on opening them, even if it begins to rain.