The Kariba hydroelectric scheme on the Zambezi River border between Zambia and Zimbabwe. Repairs are scheduled to start in the second quarter of next year. Picture: REUTERS/MACKSON
By Tom Nevin, Business Day Live
THE rehabilitation of the Kariba hydroelectric scheme on the Zambezi River border between Zambia and Zimbabwe could provide a fillip for the southern African economy. Apart from the R3.3bn cost of the repair work to the dam, hundreds of millions of dollars could be spent on other development projects.
French companies tendering for Kariba’s rehabilitation programme say if their bid is successful, they will partner with Zimbabwe’s private sector to help rebuild the country’s economy, while other countries in the region will benefit from the spin-offs.
French Agency for Development regional director Martha Stein-Sochas says a slew of construction companies have tendered for the project.
The European Union’s (EU’s) head of delegation to Zambia, Gilles Hervio, says the union’s contribution to the project is part of a wider joint strategy with Zambia to improve access to clean, reliable and affordable energy.
"Overall, the EU has set aside €244m for this purpose in the national indicative programme for Zambia for the period 2014 to 2020," he says.
"We are preparing a wider package of technical assistance for Zambia, including transfer of expertise and innovative technologies, with a view to strengthening energy policies, regulatory framework and supporting different institutions working in the energy sector."
Mozambique’s people and businesses would stand to benefit from energy upgrades in the region.
The Kariba rehabilitation programme is being administered by the jointly-owned Zambia-Zimbabwe Zambezi River Authority and financed by the EU, the World Bank, the African Development Bank and the Swedish government.
The work will include the reshaping and stabilisation of the dam’s plunge pool — an 80m deep crater encroaching on the dam wall’s foundations. About 300,000m³ of rock will be excavated from the pool to produce a stepped profile that will increase energy dissipation and guide the water downstream, away from the foundations. Kariba Dam’s spillway system will also be refurbished.
A World Bank report says the work "is unprecedented in dam history and urgently needed to prevent any potential further regression". Hervio says the project "will ensure people’s safety and prevent one of the potentially worst disasters".
The work is scheduled to start in the second quarter of next year, at the end of the rainy season.
New precautions are being taken to lessen vibration shocks on the structure. Weight limits have been placed on heavy vehicles using the dam-wall road to lessen stress on it.
The Chinese government has agreed to give $316m to upgrade Zimbabwe’s Kariba South Bank Power Station’s generating capacity from 750MW to 1,050MW.
It enhanced Zambia’s North Bank Power Station, adding 360MW, for a total capacity of 1,080MW.
Cyril Manyoni, solutions engineer at Pragma — a multinational physical asset management solutions provider in the management and optimisation of physical assets — believes the root cause of Kariba’s problems is maintenance.
HE notes when the dam was completed in 1959, the effect of the spillway water on a fault in the granite bedrock immediately downstream was underestimated. "Although there was a plunge pool, it was not sufficiently deep or wide to safely dissipate the energy of the water out of the spillway," he says. "Studies and investigation into the effects of ASR (alkali-silica reaction in concrete) only started in the last two decades.
"Such bodies as the International Commission for Large Dams and the American Concrete Institute were at the forefront, with work largely focused on ways and means to mitigate, if not reverse, such deterioration because most dams in use today are more than three decades old.
"It is a fact conceded by the Zambezi River Authority that their maintenance is not on par with current global best practice, whether by choice or circumstance, which could also be a further point of argument. A dam wall is a physical asset which, like most other physical assets, is designed using the best technology and knowledge available at the time."
Manyoni says there should be a thorough, systematic approach to optimal operation and maintenance, with a view to extending Kariba’s life, but that such physical assets have "a life of asset" and should be disposed of once they have returned their investment.
Kariba’s sell-by date was probably about 2010. Its owners, Zambia and Zimbabwe, have kept it going in the hope, it seems, of coaxing "another few decades out of it with the help of a R3bn repair job", according to a Kariba businessman.
"More often than not," says Manyoni, "the asset owner does not keep abreast with global standards in physical-asset management best practice."
Unless an all-out effort is made, it is possible the World Bank’s prediction — shared by government officials from Zambia and Zimbabwe, the river authority, as well as local and international engineers — that a calamitous event will be visited on the people and assets of the Zambezi Valley.
Bernard Goguel, an engineer with Kariba’s designers, French engineering company Tractebel, who was the assigned surveillance engineer of the giant hydro scheme between 1987 and 2010, takes issue with the claim that the plunge pool was smaller 10 years ago than it is now.
"Its development was carefully inspected and monitored year after year," he says, adding that there were no spillages between 1982 and 1999, due to low inflows from the Zambezi River.
Goguel says the plunge pool was repeatedly checked after annual spillages resumed in 2000.
"From that time, no significant change was observed or reported in the plunge pool development," he says. "Some concern had developed, nevertheless, regarding the possible adverse effects of severe, intense and long-duration spillages, which may occur in case of exceptional floods — say, beyond the 500 years return period."
THE current rehabilitation is being undertaken on a just-in-case basis because the owners have decided to enhance the dam in the interests of safety in the long term, taking care of the two major maintenance issues of flood spillway structures overhaul and plunge pool reshaping, Goguel says.
He insists that there is "no immediate danger of collapse at Kariba Dam but a need to face ageing issues: structural and design ageing, in the light of experience gained during the scheme operation and regular routine inspections and maintenance".
Goguel maintains the planned works will cost less than 10% of the cost of a new dam, "which is quite defensible after 55 years of satisfactory operation". "Kariba Dam has many more years to last…. Dewatering Kariba Lake for rebuilding the dam is an unrealistic and unnecessary dream."
After the R3.3bn rescue is completed, the dam’s owners will look another conundrum in the eye — what to do with Kariba when big dams are no longer needed. Abundant fusion energy might be available soon, or there could be a breakthrough in hydrogen cell technology, making other means of electricity generation redundant.
International hydro-scheme consultant Bryan Leyland has studied Kariba and Egypt’s Aswan Dam looking for answers to such questions. He believes the cost of dewatering Kariba could run to $3bn-$5bn and would be a waste of money.
The biggest dam dewatered so far is the 65m high Glines Canyon Dam in Washington State, US. The three-year process was completed in August and followed a court injunction for the dam’s demolition to restore traditional salmon runs and shellfish breeding grounds.
"The more we think about it, the more we realise the great difficulty in de-commissioning big dams and Kariba is a classic case in point," says Leyland.
"Kariba and Aswan might as well be called the ‘forever dams’ because chances are we’ll never be rid of them."