Name of the Project
Kariba dam rehabilitation project (KDRP).

Location
Zambia and Zimbabwe.

Project Owner/s
The Zambezi River Authority (ZRA) operates, maintains and manages the Kariba dam on behalf of the governments of Zambia and Zimbabwe.

Project Description
After almost 60 years of serving the Southern Africa region, the Kariba dam requires rehabilitation to ensure its longevity.

The natural riverbed immediately downstream of the dam has eroded into an 80-m-deep plunge pool, as a result of routine heavy spillage of floodwater over the years. The erosion, instead of taking the expected downward trend, has also progressed towards the dam foundation, following a rock fault that had not been detected during the design and construction of the dam. Routine monitoring and the implementation of routine interventions, such as crevice underwater repairs and controlled spillage, have slowed the natural erosion. No significant changes to the plunge pool depth and shape have been recorded in the past 15 years.

The erosion has threatened to undercut and destabilise the foundations of the wall.

An analysis of the monitoring results by the ZRA has also shown continuous swelling of the wall concrete, owing to slow chemical reactions – alkaline aggregate reaction – over the years. This has affected the smooth and safe operation of the spillway gates. In the longer term, additional swelling could cause the spillway gates to jam. Failure to invest in the timely rehabilitation of the dam will result in the gradual deterioration of the key safety features associated with the structure.

Rehabilitation measures include:

• the design, fabrication and installation of an emergency gate and a new gantry to prevent the uncontrolled loss of water in the event of floodgate failure, which will result in water levels dropping to below the minimum operating levels and interrupt power production;

• the refurbishment of the upstream stop-beam guides and the replacement of secondary concrete to prevent failure during the operation of stop-beams; and

• reshaping the plunge pool downstream of the dam to limit scouring and erosion that could potentially undermine the dam foundations, leading to dam failure.

Potential Job Creation
The KDRP will create some job opportunities for skilled, semiskilled and general workers, particularly pertaining to the plunge pool reshaping.

Capital Expenditure
The total project cost was estimated at $294-million, which will be released in tranches spread over the duration of the project. The project is being funded by the European Union (EU), the World Bank, the African Development Bank (AfDB), the government of Sweden and the ZRA, on behalf of the governments of Zambia and Zimbabwe.

Planned Start/End Date
Despite some delays encountered during implementation, in particular unforeseen geological complexities, the project, which started in May 2017, remains on course for completion by the end of 2024.

Latest Developments
ZRA is progressing with work on the KDRP.

From inception, the project’s objective has been to ensure the enhancement of the structural integrity of the Kariba dam, thereby ensuring sustainable generation of power primarily for the benefit of Zimbabwe and Zambia’s citizens, as well as the entire Southern African Development Community region.

Work on the reshaping of the plunge pool, which includes bulk excavation of the rock in the existing pool to facilitate the stabilisation of the plunge pool and prevent further scouring or erosion along the weak fault zone towards the dam foundation, is progressing well. This work will be achieved through construction of a temporary water-tight cofferdam to facilitate the reshaping works under dry conditions.

Work on the project is currently 60% complete.

The ZRA has reported that its spillway refurbishment works are also progressing well.

These works are meant to replace secondary concrete and built-in-parts  of upstream guide slots of the stop beams, and to ensure the free movement of the electromechanical equipment that is used to block the flow of water from the upstream face-of-the-dam wall.

An emergency gate to close the sluices under emergency conditions (to be used where a gate fails to close after release of excess flood water) is also being manufactured.

This project, which started in November 2019 and is being implemented by a consortium that includes GE Hydro and Freyssinet International, is targeted for completion in January 2025.

Further, the ZRA has said that while consistent measures have been adopted and implemented to mitigate the effects of Covid-19 on the KDRP, the project has been impeded, following negative impacts on site arrangements, offshore supplies and logistics.

The impacts include loss of time, as a result of returning expatriates and other local employees having to be quarantined each time they were diagnosed with the virus.

The failing of the owner and owner’s engineer to timely witness the factory acceptance tests (FATs) and vendor quality surveillance (VQS) for the KDRP’s equipment before such equipment could be approved and shipped to the project site has also impacted negatively on the project.

The prevalence of Covid-19 also led to stricter border-crossing restrictions, resulting in traffic congestion, consequently affecting the timely delivery of project equipment.

These disruptions resulted in time and cost overruns against the project baseline schedule and budget respectively.

To mitigate these challenges, the ZRA reports that the project owner, through stakeholders’ support, has remained resilient in devising meaningful mitigation measures, including programme enhancement through night shifts.

The owner’s engineer representation in FATs and VQS, as well as accelerated Covid-19 vaccination and testing for the KDRP site staff, have also been instrumental in re-aligning the project to its implementation plan, the ZRA has noted.

Key Contracts, Suppliers and Consultants
EU (grant financing); World Bank and AfDB (loan and part grant financing); government of Sweden (grant financing) and Razel-BEC (plunge pool reshaping contractor); GE Hydro France & Freyssinet International (Kariba dam spillway contract).

Contact Details for Project Information
ZRA public relations and communications manager Elizabeth Karonga, tel +260 211 230551 or email karonga@zaraho.org.zm; info@zaraho.org.zm.