View Full Version : Kariba Dam 'n dreigende ramp?

02-22-2015, 06:27 PM
ENGINEERS have started on a R3.3bn rescue marathon to prevent the "catastrophic failure" of the Kariba Dam. According to a World Bank special report on the beleaguered structure — one of the biggest man-made dams in the world — a potential wall collapse threatens the lives of about 3-million people living on the Zambezi River floodplain between the hydro scheme on the Zambia-Zimbabwe border and the Mozambique coast.

The document, titled The Kariba Dam Rehabilitation Project, estimates that in the event of a "catastrophic Kariba Dam failure", economic damage to the region will exceed R88bn and will include the washing away of the Cahora Bassa Dam and the loss of 40% of southern Africa’s electricity capacity.

Although the danger was spotted a decade ago, the parlous condition of the wall only filtered out recently. The World Bank, the watchdog Zambezi River Authority and engineers are united in their opinion that, without urgent repairs, the dam will fail.

Kariba’s dam wall is under attack on two fronts. Spillway torrents have excavated a massive cavern in the Zambezi river bed that threatens the stability of the wall foundations, and a slow chemical reaction is causing concrete swelling, affecting the operation of the spillway gates and their effectiveness in handling high water levels.

In recent announcements, officials in Zimbabwe and Zambia have been at pains to reassure the public that, while the situation is serious, it presents no immediate danger. A rehabilitation programme has been drawn up by local and international engineers; funding has been raised and is in the bank.

The short timeline for the repairs is the real peril, and the scope of the work to be done is daunting and will test the skills of some of the best engineering experts assembled for the task.

Before the World Bank’s report was released in December, finding out why a blanket of silence had been thrown over the dam’s problems was hugely frustrating. Kariba’s designers, the French firm Coyne et Bellier (now known as Tractebel Engineering) did not respond to inquiries.

Tractebel’s website notes that after the reservoir’s filling in 1960, Coyne et Bellier was assigned to regular checkup missions, monitoring and technical assistance. "We performed five annual inspections and, if needed, specific calculations," it says.

Between 1963 and 2010, project management was performed by Bernard Goguel, an internationally renowned expert on dam surveillance. "In 2010, a new contract was signed. Tractebel Engineering now advises the Zambezi River Authority on matters pertaining to safety, maintenance and satisfactory operation of the dam. It includes engineering studies and works supervision of the spillway rehabilitation, construction of an emergency gate, and sustainability of the plunge pool."

It is now known that the problem was noticed at least 10 years ago when the pit was smaller than it is now and the floodgates were showing signs of stress.

Details of the dam wall’s weakness filtered out into the tightly knit lakeside community last year, setting off alarm bells. In response, statements were issued by officials, local bodies and politicians — for the most part wildly contradictory, creating much of the alarm and confusion.

The Zambian Engineers Association and the Zambezi River Authority insisted there was no immediate danger, while politicians painted a more dire picture.

The authority’s communications manager, Elizabeth Karonga, says politicians were trying to convey to outside funding agencies the urgent need for major rehabilitation of the dam. She insists, however, that while the situation is "cause for grave concern, the engineers on the ground have the situation under control. All urgency is expected in order to avert any such catastrophe as dam failure."

Local opinion holds, however, that some public announcements were aimed at "rattling the cages of international funders", as a Kariba businessman puts it.

"And it worked. It got their attention and after that money for repairs came quite quickly, all $300m."

Major funding agencies were quick off the mark with the European Development Bank providing $100m, the World Bank $75m, the Swedish government $47m and the African Development Bank $75m for a $295m emergency package after a team was sent to inspect the dam.

Financing the dam wall’s rehabilitation is a sticky proposition. While Zambia is entitled to financial assistance from the international donor community, Zimbabwe is not. But it is not possible to repair only one side of the dam and Zimbabwe will benefit from any repair work. ......................................



02-22-2015, 06:31 PM
Nog so 'n stukkie uit die berig:

Kariba’s real race is against that great enemy — time. The consensus of engineers from around the world is that Kariba has a life span of three years if extensive repairs are not undertaken immediately. Southern Africa and the world must sit up, listen and take action in both reconstruction and finding, in all probability, a lot more funding than the R3bn already at hand.