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'Muela hydropower tunnel


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The 60m long, 15m wide by 30m high cavern

Power generation

Mott MacDonald was appointed by Lesotho Highlands Development Authority, in joint venture with Lahmeyer International, to provide consultancy services for the 'Muela hydropower station which forms the power generation component of the £1.5 billion Lesotho Highlands Water Project. The £70 million hydropower station is the first electric power generator in the Kingdom of Lesotho, making the country self-sufficient in electricity. The project – commissioned in 1998 – was financed by the Government of Lesotho, African Development Bank and the European Development Fund.

Value management
The joint venture's remit included all civil, mechanical and electrical engineering associated with the power station. The first step was a thorough review of the tender design which resulted in extensive changes reducing the cost of the works by 10%, while improving the speed of response of the power station to load changes. This was followed by detailed design, preparation of working drawings and construction supervision.

World’s longest headrace tunnel
Water will reach the underground power station via a 45km headrace tunnel which is the longest of its kind in the world. The maximum 300m hydrostatic head is used to drive three 24MW machines located in a cavern 60m long by 15m wide by 30m high, excavated in the Clarens sandstone. The water then discharges along a 1.4km tailrace tunnel to ’Muela tailpond, formed by a 55m high double curvature arch dam across the Nqoe River.

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