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Project details
Lesotho
Dam
2004

Details of the project:

Following the lessons learned from the devastating droughts of the late 1960's, a joint Technical Committee between Lesotho and South Africa was created in 1978 to do a full feasibility study on the capture and transfer of the excess flows of the upper Senqu catchment via a series of storage dams and tunnels to South Africa.
This project generated hydro-electricity for Lesotho before delivering the crystal clear mountain water to the homes and industries of South Africa. It would also create revenue for Lesotho and provide jobs.

The project was realised in different phases:

A preparation phase. Indeed, to penetrate the Highlands with the machines and equipment required for the constructing of the project called for the construction of the necessary infrastructure to host staff and drive the machines and equipment to their working sites; 4 phases of construction for the project in itself:

• Phase 1A (1995 - 1997) comprises the Katse and 'Muela dams, the hydropower station of 'Muela, the Transfer Tunnel and Delivery Tunnels, as well as the Ash River Outfall.
• Phase 1B (1997 - 2004) comprises the Mohale Dam, the Interconnecting Tunnel, Matsoku Weir and the Matsoku Tunnel.
• Phases 2, 3 and 4: construction of the Mashai (170 metres high), Tsoelike and Ntoahae dams.

Details of the project constructions CHRYSO participated in:

The concrete arch of the Katse dam, which is the highest double curvature, concrete arch, gravity dam in Africa at a 185 m height. The prefabricated ring segments of the Mohale tunnel, 31.6 km long, which links Mohale dam to the reservoir. It was designed to provide an outflow of water at the average rate of 9.5 m3/s. This channel, 31.6 km long, is navigable and fully lined with a facing, half of which is underground and of a 4.66 m diameter, whilst the other half has a 4.25 m diameter. The supply of the channel is located in the Mohale reservoir, two sections designed to be submerged. Two shafts, one at each extremity, allow the supply and discharge channels to be isolated from the main channel.The latter is located underground. The weir is sealed by a metallic partition. A gravitational supply channel, 6.4 km long, takes water from the dam of the river Matsoku to the reservoir.

The main aim of the concrete realised is optimal water tightness.

Concrete formulation:
• Total volume of concrete: 2 600,000 m3 for the whole project, 200,000 m3 for the transfer tunnel.
• Specifications: Maximum water reduction associated with a workability suitable to place good concrete. Compressive strength: 3 MPa at 8 hours.Concrete to be pumped over a 200 m distance

Project participants :

• Designer: Lesotho Highlands Consultants consortium.
• Owner: Lesotho Highlands Development Authority
• Contractor: Highlands Water Venture, Spie Batignolles, Campenon Bernard, Zublin, Balfaur Beatty & LTA
• Companies: Hochtief, Impregilo & Concor.
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