Construction
The power station machine hall was excavated from solid granite rock 200 metres below the level of Lake Manapouri. Two tailrace tunnels take the water that passes through the power station to Deep Cove, a branch of Doubtful Sound, 10 km away. Access to the power station is via a two-kilometre vehicle-access tunnel which spirals down from the surface, or a lift that drops 193 m down from the control room above the lake. There is no road access into the site; a regular boat service ferries power station workers and tourists 35 km across the lake from Pearl Harbour, at the eastern end of the lake.
The original construction of the power station cost NZ$135 million (NZ$1.95 billion in 2008 dollars), involved almost 8 million man hours to construct, and claimed the lives of 16 workers.
Soon after the power station began generating at full capacity in 1972, engineers confirmed a design problem. Greater than anticipated friction between the water and the tailrace tunnel walls meant reduced hydrodynamic head. For 30 years, until 2002, station operators risked flooding the powerhouse if they ran the station at an output greater than 585 MW (with high lake level and a low tide the station could generate up to 603MW), far short of the designed peak capacity of 700 MW. Construction of a second tailrace tunnel in the late 1990's, 10 km long and 10 metres in diameter, finally solved the problem and increased capacity to 850MW. The increased exit flow also increased the effective head, allowing the turbines to generate more power without using more water.
Read more about this topic: Manapouri Hydroelectric Power Station
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—Gus Van Sant, U.S. screenwriter and director, and Dan Yost. Bob Hughes (Matt Dillon)