Work on the long-awaited rehabilitation of the Kariba Dam wall, which hosts the giant Kariba Hydro-Electric Station that generates electricity for Zimbabwe and Zambia is set to commence in February 2017, the Zambezi River Authority (ZRA) has announced.
Addressing journalists in the southern Zambian town of Livingstone this week, ZRA chief executive officer, Munyaradzi Munodwafa, said work on the main component, which would be focused on a re-modelling of the plunge-pool to minimise a scouring of its foundations, would commence in February 2017 and continue up to early 2020.
Advanced repair works on all six spill-way gates around the dam wall are set to commence in July 2017 and continue up to July 2024. As of April 2015, the total project cost was estimated at US$ 294 million, which would be released in batches spread over the duration of the works.
“Tenders for the contractors to carry out works on the plunge pool will close on October 23, 2016, and for the sluice gates tenders will be opened in November while the bidder is expected to be appointed by June next year. Without functional sluices, the reservoir level cannot effectively be maintained to take into account the flood regime of the Zambezi River,” he said.
The project was funded by partners who include the European Union, the World Bank, the African Development Bank and the government of Sweden to help the governments of Zimbabwe and Zambia avert a possible collapse of the dam wall.
Apart from economic losses arising from the destruction of the hydro-power investments, a collapse of the Kariba Dam wall would generate a regional humanitarian crisis arising from flooding.
The rehabilitation followed the recommendations of a ZRA-commissioned expert assessment which found that the structural integrity of the 55-year-old dam wall had been compromised through the years by an erosion of the plunge pool, with the foundations chipped down to depths of up to 90 metres beyond permissible levels through advanced alkali-silica reaction in the concrete.
The erosion had under-cut and destabilised the wall, putting the entire wall structure at high risk of collapse. The expert report also warned that a continuous swelling of the concrete wall, due to slow chemical reactions over the years, was constricting the passage of water through the spillways.
Such a constriction of the spill-ways could obstruct the reservoir’s water level control systems and lead to an excessive build-up of pressure on the weak wall and potentially precipitate its collapse.
Apart from the loss of the two hydro-electric plants, a collapse of the wall also posed a massive risk of flooding in Zimbabwe, Zambia, Malawi and Mozambique in the event of the Zambezi River bursting its banks due to a sudden emptying of the 250km-long water reservoir, which makes up Lake Kariba.