Name of the Project
Kariba dam rehabilitation project.
Location
Zambia.
Client
Zambezi River Authority (ZRA), a joint venture between Zambia and Zimbabwe, the African Development Bank (AfDB), the European Union, Sweden and the World Bank.
Project Description
After 50 years of serving the Southern Africa region, the Kariba dam requires a series of rehabilitation works for its continued safe operation.
The structural integrity of the 55-year-old dam wall has been compromised through the years by erosion of the plunge pool, with the foundations chipped down to depths of up to 90 m beyond permissible levels through advanced alkali-silica reaction in the concrete.
The erosion has undercut and destabilised the wall, putting the entire wall structure at high risk of collapse. An expert report produced by the ZRA has also warned that a continuous swelling of the concrete wall, owing to slow chemical reactions over the years, is constricting the passage of water through the spillways. Such a constriction of the spillways 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.
Failure to invest in the timely rehabilitation of the dam will result in the gradual degradation of key safety features associated with the structure to a level that is not acceptable in accordance with international standards.
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 interrupting 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.
The Kariba dam is one of the world’s largest hydrodams, generating more than 1 300 MW of hydropower. The dam’s wall, which is 128 m high, straddles Zambia and Zimbabwe. Should it collapse, flooding from the Zambezi river could affect parts of Zambia, Zimbabwe, Malawi and Mozambique, affecting millions of people.
Jobs to be Created
Not stated.
Value
As of April 2015, the total project cost was estimated at $294-million, which will be released in batches spread over the duration of the project.
The project is being funded by the European Union, the World Bank, the African Development Bank and the government of Sweden.
Duration
The Kariba dam faces collapse if not repaired in three years.
Latest Developments
Work on the Kariba dam wall, which hosts the giant Kariba hydroelectric power station, is set to start in February 2017, the ZRA has announced.
Advanced repair works on all six spillway gates around the dam wall are expected to begin in July 2017 and continue until July 2024.
Tenders for the contractors to undertake work on the plunge pool will close on October 23, 2016. The tender for the sluice gates will be opened in November, with the bidder expected to be appointed by June next year.
Key Contracts and Suppliers
AfDB (loan finance).
On Budget and on Time?
Not stated.
Contact Details for Project Information
ZRA, tel +260 1 228401, fax +260 1 227498 or email zaraho@coppernet.zm.
AfDB senior power engineer Elizabeth Muguti, email e.muguti@afdb.org.