Southern Africa Watch

Possible inland tsunami from Kariba has Southern Africa on tenterhooks

Kariba Dam – urgent repairs needed
Kariba.jpg

There is concern that the Kariba Dam might fail sometime in the foreseeable future – with devastating consequences. The official message refutes this doomsday scenario. What is the real situation?

The recent unexpected luxury of five weeks without load shedding ended with the announcement that South Africans should prepare for the inevitable, with supply from Mozambique’s Cahora Bassa hydroelectric scheme to be reduced due to maintenance.

It was, however, of little comfort to be told that the supply would be restored as soon as the maintenance was completed. A much more serious calamity, emanating from Kariba Dam higher up in the Zambezi River, might await Southern Africa.  

If not checked, it could result in the destruction of Cahora Bassa, eliminating 40% of Southern Africa’s hydro-electric capacity, cause severe flooding, the death of up to 3.5 million people and have a severe impact on the lives of 30 million people and their basic needs.

It is conservatively estimated that the collective economic damage to the affected region will exceed R88 billion. 

What is at stake?

The cause of the concern is the urgent reparation needed on the crumbling 128-metre dam wall at Lake Kariba, due to erosion of its basalt foundations.

Torrents from the dam’s spillway eroded the seemingly solid bed of basalt the dam was built on and a large crater has formed, undercutting the dam’s foundations. Emergency spilling has, over the years, caused a plunge pool of about 80 metres deep, some 50 to 75 metres downstream of the wall – already 10 times bigger and deeper than the original design.

Details of the dam wall’s weakness became known piecemeal, setting off alarm bells. Statements about the situation from officials, local bodies and politicians have been wildly contradictory, causing even more alarm and confusion.

The World Bank, the management of the Kariba Dam, the Zambezi River Authority (ZRA) and engineers are united in their opinion that, without urgent repairs, the Kariba Dam will fail.

Reports from many sources claim that “if nothing is done, the Kariba Dam will collapse in three years”. 

According to experts, failure to perform the required rehabilitation would result in the release a ‘tsunami’ of water through the Zambezi Valley when the wall collapses. It will reach the Mozambique border within eight hours, demolishing Cahora Bassa Dam and everything else in its path.

Differing opinions

There are, however, widely differing thoughts on this doomsday scenario.

The ZRA gave assurances that the required reparations will be made before disaster strikes. In recent announcements, officials have been at pains to reassure the public that, while the situation is serious, it presents no immediate danger.

The real peril is the short timeline for repairs. The scope of the work to be done is also daunting and will test the skills of the engineers and repair team assembled for the task.

The reshaping of, for example, the plunge pool into which water from the sluices is discharged at a peak of 8 000 tonnes per second, and the repair work to the dam’s six floodgates, require the construction of a temporary cofferdam or barrage. This is required to enable blasting and excavation of 300 000 cubic metres of rock from the downstream face and the north and south bank sides of the pool during the dry season.

This work was scheduled to start in May 2015, after the rainy season, but according to media reports it will now only commence in September 2015.

Engineering masterpiece

Built in only four years some fifty years ago, the world's largest man-made reservoir, with a capacity of holding 181 billion cubic metres of water, remains an awesome engineering feat. 

“A masterpiece of engineering skill,” was British Queen Elizabeth’s apt description, at the inaugurating ceremony in 1960, of the subjugation of the mighty Zambezi.   

Well over a million cubic metres of concrete was poured into the wall to withstand the sustain pressure of nearly ten million litres of water passing through the spillway each second.

The dam’s contribution to nature conservation is also remarkable. Between 1958 and 1961 Operation Noah captured and removed around 6 000 large animals and numerous small species threatened by the lake’s rising waters – lessons learnt then in the capturing and relocation of wildlife are still practised today.

The Kariba keeps two hydropower stations going. On the north bank is a power station with an installed capacity of 1 080 megawatts (MW) and on the south bank a 750MW-facility, which will, by completion of projects currently underway, increase to 1 050MW by 2018.

Lower down the Zambezi, Cahora Bassa’s installed capacity is 2 060MW, much of which is transmitted to South Africa.

Urgent rehabilitation

Political foot-dragging and interference and, especially, poor management are the main reasons for the alarm and the urgent repair work.

The rehabilitation project for the Kariba Dam is expected to cost US$300 million over 10 years – cheap, compared to the around US$5 billion a new Kariba would cost.  

Most of the required funding for the project has already been secured from the African Development Bank, the World Bank, the European Union and the Swedish government.

Consequences      

Should the unthinkable happen, the following scenario is the most likely, according to the findings in a report ‘Impact of the Failure of the Kariba Dam’:

“The reduction in the supply of electricity to various countries in the region will be significant and immediate. Some countries rely totally on hydropower and their economies will be seriously impacted, both for industries that rely on electricity to operate and in terms of revenue generated from the sale of electricity.

“South Africa will lose 1 500MW of imported power as the Cahora Bassa Dam fails. Access to water for people in the Kariba and Cahora Bassa Dam areas for drinking, food and agriculture will be severely restricted while transportation and access to the areas affected will be curtailed, alternative routes across the Zambezi will need to be sourced, leading to increased cost and time for deliveries.”

It is also estimated that Southern Africa will experience an economic, social, environmental, humanitarian and technological fallout that will devastate the region’s economies for potentially up to eight years, while the dams and infrastructure are rebuilt.

The report concludes: “Whether you are a shareholder, stakeholder, board member, business executive, risk manager or even private individual, if you live, work, own property or have investments in South Africa, Zambia, Zimbabwe, Botswana, Mozambique or Malawi, the chances are that if the Kariba Dam fails, you will be affected.”

For now, we have only the word of those in charge of the Kariba Dam that there is nothing to be concerned about, that all is well at Lake Kariba.

by Garth Cilliers

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