Large-scale dams on the African continent used for irrigation or flood control are coming up to a critical age. The Kariba Dam straddling Zimbabwe and Zambia is a key example, according to a new report by the UN University Institute for Water, Environment and Health. And while climate shocks could impact the dams, ageing is also a major concern.
"A well-built, well-maintained, well-designed structure can last for quite a while, maybe more than 100 years," says Vladimir Smakhtin, director of the UN think tank on water UNU-INWEH, and co-author of the report. "We have cases of dams all over the world which are operating in this way."
According to the research, there are currently 2,000 large dams in Africa, with a quarter of them in South Africa. They are the fewest and youngest of any continent.
Large dams - those taller than 15 metres and holding more than 3 million cubic metres of water -- have a major impact on the people and the environment, and this must be carefully considered if a dam is to be decommissioned.
Repairs to Kariba
Case in point is Kariba Dam, a 128 metre-tall dam which stores 180 cubic kilometres of water straddling Zimbabwe and Zambia on the Zambezi River.
Kariba Dam, which began operation in 1959, is now in the process of being repaired.
Work on its should be completed by 2023. It needs to be continually maintained as an investment in its hydroelectricity capacity, says Smakhtin.
Its construction was quite controversial at the time, as 15,000 people were removed from the area and they became what one anthropologist called "development refugees."
Although large dams can be called into question, water storage on the African continent is essential, says Smakhtin, especially in countries where agricultural growth varies depending on rainfall if there is no dam.
Dams can also be used for hydropower, like Kariba, but Smakhtin predicts that this will change in the next 20-30 years due to the new renewable and environmentally friendly types of energy, including solar power.
Deactivating a dam not an option--yet
It would be too risky to decommission a dam such as Kariba, as there are a number of other dams, and thousands of people living around the dam and downstream, says UNU-INWEH Director Smakhtin.
"The world doesn't have experience of how to decommission, let alone remove such structures-- it's too risky," he told RFI, adding that smaller dams have been decommissioned globally, just not ones of this scale.
"In the case of Kariba Dam, it will definitely be a risk for the downstream communities. The societal impact of large dam removal in developing countries is very different to those which are in the north," he adds, maintaining that Kariba remains an important energy supply for the region.
Climate change challenges
A large dam built at least 50 years ago would be constructed under pre-climate change conditions, and may not necessarily be operating in the conditions it was designed for, says Smakhtin.
"That creates additional risk or uncertainty-- at the very least at how it will behave under conditions of a huge unexpected flood. It's really unpredictable," he says, adding that dam management takes this into consideration during operations.
If the rain pattern changes, and in many cases, it has, it can affect erosion of a dam structure and even accelerate the deterioration process, because it brings more silt and sediment into the dam.
"If more sediment goes into the dam, then the dam will be filled with sediments quicker and lose its functionality quicker," he says.
"And if the temperature continues to increase, then you are losing water faster, so it's less efficient," he adds.