AfDB Boosts Efforts to Save Kariba Dam

The completion of the Kariba Dam in 1959 was hailed as an extraordinary feat of man’s ingenuity in his quest to tailor the forces of nature to suit his needs.

The mines on the Copperbelt and hundreds of communities in the country and in neighbouring Zimbabwe stood to benefit from hydro-electricity that the dam was meant to generate.

But 55 years later, the forces of nature that were thought to have been tamed have returned to haunt the project and pose an engineering puzzle that has never been seen before in dam engineering in the world.

After being approached to provide financial support required in saving Kariba Dam which is jointly owned by Zambia and Zimbabwe, African Development Bank (AfDB) President Donald Kaberuka arrived in Zambia on Tuesday, 22nd July, 2014. He was on a mission to, among other things, see for himself the structural danger that has left Kariba Dam on the verge of collapse.

The AfDB, which was founded in 1964, is a multilateral development finance institution established to contribute to the economic development and social progress of African countries. It is comprised the African Development Bank, the African Development Fund and the Nigeria Trust Fund.

It was founded to fight poverty and improve living conditions in Africa through promoting investment of public and private capital in projects and programmes that are likely to contribute to the economic and social development of African states.

The Tunisia based bank which was originally headquartered in Abidjan, Ivory Coast, is a financial provider to African governments and private companies investing in regional member countries.

The bank is currently considering a request to fund construction of the US$259 million Kazungula Bridge across the Zambezi River between Zambia and Botswana.

The banks concern in the Kariba Dam scenario arises from the multiple economic threats that a weakened Kariba Dam poses to the whole of Southern Africa.

Firstly, an estimated 3.5 million people could have their communities flooded downstream in Malawi, Mozambique, Zambia and Zimbabwe.

This could mean widespread loss of lives and property.

Secondly, Southern Africa is already facing an electricity supply deficit.

A removal of 1,300 Megawatts of electricity generated by the Dam for both Zambia and Zimbabwe would worsen an already compromised situation.

Thirdly, any damage to Kariba Dam would endanger the Cabora Bassa downstream which houses a hydro-electric facility on the Zambezi River in western Mozambique.

Experts have said Cabora Bassa, which supplies nearly 40 per cent of electricity in Southern Africa, would either be crippled or destroyed by any damage to Kariba Dam.

Fourthly, damage to Kariba Dam would affect livelihoods of communities and commercial entities that depend on it for tourism and fishing by destroying the flourishing tourism activities upstream in Zambia and Zimbabwe, as well as the prevalent wildlife upstream and downstream.

This is one disaster the AfDB is not willing to see happen. Dr Kaberuka’s four-hour trip to the border town of Siavonga to visit the Kariba Dam on Thursday, July 24th was preceded by a meeting at which engineers from Zambezi River Authority (ZRA), which manages the dam on behalf of Zambia and Zimbabwe, described the deterioration of the 55-year old dam.

Dr Kaberuka was accompanied by Finance Minister Alexander Chikwanda, Mines, Energy and Water Development Minister Christopher Yaluma and his Permanent Secretary Charity Mwansa and other senior Government officials. They were later joined by a Zimbabwean delegation led by Finance and Economic Development Minister Patrick Chinamasa, Energy and Power Development Minister Dzikamai Mavhaire and his Permanent Secretary Patson Mbiriri. Dr Kaberuka and the two delegations from Zambia and Zimbabwe heard that the double curvature concrete arch was built between 1955 and 1959 by an Italian company.

It was built across the Zambezi River at Kariba Gorge, on the border between Zambia and Zimbabwe.

It holds one of the largest man-made expanses of water in the world.

The dam stood 128 metres high with a crest 579m in length. Its six spillway gates could release 1,500 cubic metres of water per second.

The dam creates Lake Kariba, and supplies 6,700,000,000 kilowatt-hours of electricity annually. The electricity is generated by Kariba North Bank in Zambia and South Bank in Zimbabwe.

Studies and tests conducted by ZRA engineers have shown that over the years, the plunge pool below the Dam where water from the spillway gates is released onto had progressively deepened into the rock layer from 10 metres when the dam was built to more than 90 metres.

That meant instead of water from the spillway gates cascading downstream, away from the dam after hitting the plunge pool, it instead rotates within the pool, causing erosion to progress towards the dam wall instead of away from it.

“Our studies have shown that the erosion would eventually undercut the dam foundation and if it continues, it would lead to dam failure if nothing is done,” ZRA Director – Projects and Dam Safety David Mazvidza said. He said the spilling of water from the spillway gates was the cause of erosion in the plunge pool.

“The last time all the spillway gates were opened at the same time was in 1966.

“It was done for testing. Since then, the gates have never been opened all at once because of fears that the Dam may lose its underground support due to erosion.

“That can cause the wall to collapse,” Mazvidza said, explaining that even where it becomes necessary to open the gates,

“ZRA only opens three of the six gates at any one time and even then, the gates have to be non-adjacent to reduce the water’s erosive capacity.

“Currently, we are operating the Dam unsafely,” Mazvidza warned.

He said in the short term, the two power stations on the Zambian and Zimbabwean side could be forced to cut electricity generation by between 30 to 50 per cent if the dam was not repaired soon.

This is because the water reservoirs would be depleted as a result of a compromised operating cave.

He warned that failure to take this precaution would be ‘dicing with danger’.

“This is why it is critical that repairs where done to the dam yesterday,” he said.

The ZRA plans to reshape the plunge pool by removing billions of tones of solid rock to prevent water from being trapped.

Repairs would also involve spillway refurbishment. Zambia and Zimbabwe have in the past availed US$2.5 million to the ZRA for some remedial maintenance of the dam wall and its appurtenances.

That included stability works on the south bank comprising drilling of drainage audits, surface sealing of the slope and ground re-profiling. But owing to age, repairs have become complex and more expensive for the two governments to handle.

The ZRA has also recommended that engineers urgently deal with concrete swelling which has caused the spillway gates to bend and stop opening automatically.

The gates were designed to automatically regulate the water level in the dam.

“The problem of concrete swelling was not known at the time of construction.

“What has happened over the years is that the cement used around the spillway gates has been producing a gel which expands. So we have to remove all the concrete from the spillway gates during the repairs,” Mazvidza said.

Owing to concrete swelling, the tarmac running atop the Dam wall has risen by eight centimetres since 1959.

Having seen the gravity of the state of affairs, Dr Kaberuka said AfDB would accelerate mobilization of $250 million required to rehabilitate the Kariba Dam. ‘

“I did not realise that the situation is this bad. I can assure you it will be given the urgency it deserves,” he said. Dr Kaberuka warned that if the Dam is not rehabilitated soon, the cost will be colossal.

He urged Zambia and Zimbabwe to strengthen their partnership in resolving the Kariba Dam problems, saying AfDB would continue rendering support to both countries to sustain the Dam.

He aised the two countries to ensure that studies are done thoroughly so that a good job is conducted on the dam to increase its lifespan.

He said AfDB would work with the World Bank and the European Union (EU) to pool resources required for restoring the Dam. The EU is expected to provide $100 million while the World Bank and AfDB would each contribute $75 million.

“You should ensure that technical research is carried out to ensure that proper works are done and the environmental social impact assessment is done before you begin to undertake repairs,” Dr Kaberuka said.

Successful repairs would not only remove the risk of flooding communities downstream in Malawi, Mozambique, Zambia and Zimbabwe but ensure continued supply of electricity in the region.

Mr Chikwanda echoed the need for rapid resource mobilization to save Kariba Dam, urging that, “We should move quickly and find money to rehabilitate the plunge pool.”

ZRA Council of Ministers Secretary Patson Mbiriri said the Kariba Dam plunge pool has to be remodeled and redesigned and all the six spillway gates have to be refitted to curb damage caused by concrete swelling.

Mr Mavhaire, who is ZRA Council of Ministers Chairperson, paid tribute to the Zambian Government for taking a leading role in mobilising support for the restoration of the Kariba Dam.

As engineers race towards 2015 when repairs towards restoring the Dam would begin, they are faced with a task that has only been tried in Venezuela and never been done before anywhere else in the world.

Source : The Times of Zambia

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