Threat of Imminent Kariba Dam Wall Collapse Denied

Following on the heels of the reported near collapse of the incomplete Tokwe Mukorsi dam in Zimbabwe, a certain degree of confusion surrounds the condition of the Kariba Dam on the Zambezi River, the largest river in southern Africa. It has been estimated that at least 3.5 million people in the countries of Zimbabwe, Zambia, Malawi and Mozambique are in danger should the Kariba Dam wall collapse, given that ‘serious structural weaknesses’ have reportedly developed in the wall.

Kariba Dam
Kariba Dam in 2008
Photo: Stu Haigh

Should the Kariba Dam collapse, this will reportedly lead to the destruction of the Cahora Bassa Dam, a large hydroelectric dam in Mozambique, further downstream on the Zambezi, with most of the overall casualties being in Mozambique and Malawi.

Zimbabwe and Zambia largely depend on hydro-electric power from Kariba Dam, while Cahora Bassa in Mozambique supplies 40% of the power demands in the Southern Africa region.

The Kariba Dam was constructed on the Zambezi River between Zimbabwe and Zambia in the 1950’s by the then ‘Federation of Northern and Southern Rhodesia and Nyasaland’ (Zambia, Zimbabwe and Malawi). At the time it was one of the world’s largest dams, with a wall measuring 128m (420ft) tall and 579m (633 yards) long, and a surface area of 5,400km² (2,085sqmi). Construction of the dam resulted in the resettlement of 57,000 people and many thousands of livestock and wild animals.

The permanent secretary of the Zambian Ministry of Finance, Felix Nkulukusa, was recently reported as saying that the wall of the Kariba Dam had developed weaknesses and may collapse if repairs are not commenced within the next three years.

The danger, he said, arose from an alkali-aggregate reaction in the dam wall, which could induce swelling within the concrete mass. In addition, the spillway sluice gates were no longer opening and closing automatically to maintain the required water levels, owing to distortion and swelling of rusting steel components, and erosion of the plunge pool below the sluice gates may threaten the foundations of the wall. The pool, which was initially 10m (33ft) deep, is now estimated to be 80-90m (262-295ft ) deep in places and is eroding towards the wall’s foundations.

“We are told by engineers that if nothing is done in the next three years, the dam may be swept away,” he said.

At a media briefing on 21 March 2014, Zambian Minister of Finance, Alexander Chikwanda, said that his government was aware of risks regarding the possible collapse of the Kariba dam and was working with ‘co-operating partners’ to address the problem.

The Zimbabwean state-owned newspaper, the Herald, reported the following week, however, that the Zimbabwean and Zambian governments had declared the wall stable following a tour of the dam infrastructure by senior officials from both governments.

Reading a joint communiqué on behalf of the two governments on 25 March 2014, Zimbabwean Energy and Power Development Minister Dzikamai Mayhaire said the dam was monitored and maintained in line with international standards. He said that the two governments had been proactive in addressing dam maintenance and that tender designs for some of the works had been completed at the end of 2013 and that their implementation was expected to commence at the beginning of 2015.

Kariba Dam
Kariba Dam Walls in 2010. Photo JP Mckenna

“The reshaping of the plunge pool is expected to be completed by the end of 2017 whilst spillway refurbishment will take about six years as only one gate can be worked on per year so as to allow for the possibility of spilling. These works are estimated to cost US $230 million,” he said.

According to the communiqué, the analysis of data from instruments installed in the dam during construction and thereafter, coupled with visual inspections, observations and evaluation of the dam’s safety “in line with the current practices in dam engineering”, had provided early warning of potential risks to the safety of the dam wall “long before they occurred”.

In a short statement, David Mazvidza, projects and dam safety director for the joint Zambia and Zimbabwe Kariba dam regulatory body, the Zambezi River Authority (ZRA), described the cracks in the dam wall as ‘superficial’ and said they only existed on the surface of the concrete.

“We would like to inform the public that comments in the media which said Kariba Dam wall faces collapse were made during a roundtable discussion with co-operating partners. Scenarios were presented on what could happen should rehabilitation works not be taken up with urgency”, he said, adding that there was no need for alarm.

This sentiment was echoed by Christopher Yaluma, the Zambian Mines Energy and Water Development Minister.

In a separate report, Elizabeth Karonga, communications manager of the ZRA, was quoted as saying that cracks in the structure of the dam wall were noted in 2010, and that engineers are in the process of modelling proposals for repair of the sluices and plunge pool.

The EU is understood to have undertaken in February 2014 to provide between US$85m and US$100m in July and the African Development Bank is to attempt to contribute a further US$75m. A follow-up meeting is to be held with the ‘co-operating partners’ in June.

Sources: News 24; News Day; New Zimbabwe; Lusaka Times; Herald Zimbabwe; Rapport

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