Safety concerns over Kariba Dam
Dear Sir,
It is frightening that the population of southern Africa is blissfully unaware of a potential monumental disaster that could devastate and change the face of the sub-continent for decades. Both Zambia and Zimbabwe, where the ageing Kariba Dam is located, cannot raise the funds to undertake urgently-needed massive repairs, after years of neglect to pre-empt a wall collapse.
The dam wall is slowly inching towards possible collapse. The 50-year-old, 128m-high wall is showing signs of erosion.
A collapse of the dam wall could imperil the lives of 4mn people in Mozambique, Zambia, Malawi and Zimbabwe.
The hydroelectric dam is in the Kariba Gorge of the Zambezi river basin between Zambia and Zimbabwe.
In the event of a total wall collapse, waters would move at tremendous speed and could envelop an area about 150km away within seven hours.
International engineers plan to reshape and stabilise the plunge pool at the bottom of the dam to reduce erosion at its base, which could lead to its collapse.
When the dam was completed in 1959, engineers estimated that the water pool would stretch for a maximum of 10km but it has spread about 90km, exerting enormous pressure on the beleaguered dam wall. The world’s largest man-made lake holds 181bn cu m of water.
Swelling of the concrete wall due to chemical reaction over the years is impeding the flow of water through the flood-gates.
Defects at the dam have also led to concerns about the risk of earthquakes, because the structure sits at the southern end of the Rift Valley, a tectonically active area where there have been at least 20 tremors of a magnitude greater than five.
In the worst-case scenario, a complete breach of the Kariba Dam wall could send 180bn tonne of water towards the Cahora Bassa Dam, destroying it in the process.
A wall of water more than four times bigger than the biggest tsunami on record would gush through the Zambezi valley. The destruction would be catastrophic, millions of animals would be drowned and roads, rail lines and towns destroyed.
Southern Africa’s hydroelectric capacity will drop by 40% in such a case. South Africa will lose 1,500MW of capacity.
An event of this magnitude could plunge southern Africa into darkness.
A dam failure in China, during 1975, killed 171,000 people; 11mn people lost their homes.
The sudden loss of power then was 18gw, the power output equivalent of roughly nine large modern coal-fired power stations.
Farouk Araie, [email protected]
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