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Large-scale dams on the African continent used for irrigation or flood control are reaching a critical age. The Kariba Dam, which straddles Zimbabwe and Zambia, is a key example, according to a new report from the United Nations University Institute for Water, Environment and Health. And while climatic shocks could have an impact on dams, aging is also a major concern.
“A well-built, well-maintained and well-designed structure can last for some time, perhaps over 100 years,” says Vladimir Smakhtin, director of the United Nations Water Think Tank UNU-INWEH, and co-author from “We have cases of dams all over the world that work this way.”
According to research, there are currently 2,000 large dams in Africa, a quarter of which are in South Africa. They are the smallest and youngest of all the continents.
Large dams – those over 15 meters high and containing over 3 million cubic meters of water – have a major impact on people and the environment, and this must be carefully considered if a dam is to be downgraded.
Repairs in Kariba
The Kariba Dam, a 128-meter-high dam that stores 180 cubic kilometers of water straddling Zimbabwe and Zambia on the Zambezi River, is a case in point.
The Kariba Dam, which began operating in 1959, is currently under repair.
The works are expected to be completed by 2023. It is to be continuously maintained as an investment in its hydropower capacity, Smakhtin said.
Its construction was quite controversial at the time, as 15,000 people were expelled from the area and became what one anthropologist called “development refugees”.
While large dams can be challenged, water storage on the African continent is essential, says Smakhtin, especially in countries where agricultural growth varies with rainfall if there is no dam. .
Dams can also be used for hydropower, like Kariba, but Smakhtin predicts that will change in the next 20-30 years due to new types of renewable and environmentally friendly energy, including solar power.
Deactivating a dam is not an option – for the moment
It would be too risky to take a dam like Kariba out of service, as there are a number of other dams and thousands of people living around the dam and downstream, said UNU-INWEH director Smakhtin. .
“The world has no experience with decommissioning, let alone removing such structures – it’s too risky,” he told RFI, adding that smaller dams have been downgraded in the world, but not those on this scale.
“In the case of the Kariba dam, it will certainly be a risk for communities downstream. The societal impact of removing large dams in developing countries is very different from those in the north, ”he adds, saying Kariba remains an important energy supplier for the region.
The challenges of climate change
A large dam built at least 50 years ago would be built under pre-climatic conditions and wouldn’t necessarily work under the conditions for which it was designed, Smakhtin says.
“It creates additional risk or uncertainty – at least as to how it will behave under the conditions of a huge unanticipated flood. It’s really unpredictable, ”he said, adding that the management of the dam takes this into account during operations.
If the rainfall regime changes, and in many cases, it can affect the erosion of a dam structure and even accelerate the deterioration process, as it brings more silt and sediment into the dam.
“If more sediment enters the dam, then the dam will be filled with sediment faster and lose functionality faster,” he says.
“And if the temperature keeps rising, you lose water faster, so it’s less efficient,” he adds.
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