The Kariba double curvature concrete arch dam was built in the late 1950s on the Zambezi River, which forms the border between Zambia and Zimbabwe. The Kariba dam forms the world’s largest artificial reservoir with 181 billion cubic metres of water. The dam is 128 m high with a crest length of 617 metres and supplies two underground hydropower stations with a total capacity of 1830 MW providing a little under 50% of the power to each country

Since its construction, the dam has suffered from alkali-aggregate reaction (concrete swelling) which has caused an increasing risk of jamming when operating the 6 gated crest spillway gates and the corresponding stoplogs. Moreover, intense scouring of the rock foundation in the plunge pool has occurred over the decades at the toe of the dam due to the spillway jet impact, digging a hole no less than 90 m deep, which threatens to undermine the dam’s foundation.

The Kariba dam rehabiliation project - engineering design and supervision

Gruner Stucky Ltd was contracted to design and supervise the rehabilitation works for the spillway and plunge pool, with the objective of improving the safety and reliability of the Kariba Dam. The works will include the reshaping of the plunge pool to limit scouring and erosion that could potentially undermine the dam foundations and the refurbishment of the spillway and associated infrastructure to improve the dam’s stability and operations.

The project has two components:

1. Changing the gantry crane, stop-beams and vertical slots in the secondary concrete of the dam, so as to ensure the closing of stop-beams against the flow;
2. Stopping the scour development by excavating (blasting) and rendering the plunge pool into a suitable hydraulic shape, thereby increasing the water jet energy dissipation and stabilizing the regressive scouring of the dam foundation.

The works are expected to end in 2025. The video below explains the works to be done.

The project has its own website hosted by the Client the Zambezi River Authority where you can find more information : http://www.zambezira.org/kdrp/

You can also read more on the World Bank’s website https://www.worldbank.org/en/region/afr/brief/the-kariba-dam-rehabilitation-project-fact-sheet

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