Kariba Dam

Fears that Kariba Dam may collapse

The foundation of the Kariba Dam wall is eroding and has to be repaired urgently to avert a massive disaster. A large pool carved out by opening the sluice gates has eroded the integrity of the wall, which may collapse within the next three years.

If the wall collapses, it will affect 3,5million people living downstream from the dam. Power supplies to large parts of southern Africa will also be disrupted because a collapse with subsequent downstream flooding will affect two hydroelectric schemesone at Kariba and another at Cahora Bassa, which supply a combined 1500megawatts of power to South Africa.

The restoration of the dam, which was completed in 1958, will cost approximately R2.7 billion and is considered to be one of the largest and most challenging projects of its kind.

Chris Herold, the vice-president of the SA Institute of Civil Engineering, says the biggest problem is the more than 50 years of water erosion in the immersion pool at the foot of the dam’s 128m-high wall. “This is the deep pool where the lake’s huge volumes of water fall when the sluice gates are opened. Erosion takes place where the water hits the bottom of the pool–and the pool has been carved out deeper and deeper over the decades,” he adds. “The pool is already 9m deep in certain places. As the erosion cuts the pool walls wider, it cuts back into the foundation of the wall.”

As this happens, the structure of the wall becomes increasingly unstable, which could lead to it eventually collapsing. The problem is aggravated because the erosion hazard means no more than three of the dam’s six sluice gates can be opened at any one time. This halves the dam’s release capacity and if there’s a flood, only half of the water can be released. This will place additional pressure on the wall.

Elizabeth Karonga, the communications manager of the Zambezi River Authority, confirms the damage. She says a team of French engineers inspects the wall every five years. According to her, engineers are building models for the restoration of the wall and the repairs could take at least six years – one for each sluice gate.

José Matola, a specialist hydrologist at Cahora Bassa, told City Press’ sister paper, Rapport, an emergency meeting with all “relevant authorities” in Malawi, Mozambique, Zimbabwe and Zambia will be held. “We are very worried. If action is not taken quickly, the wall will break in three years’ time and we at Cahora Bassa will be hit by a huge wave against which we stand no chance at all,” he says.

Source: City Press


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