Client
New Zealand Ministry of Works
Location
Lake Manapouri, New Zealand

New Zealand Ministry of Works Manapouri Power Station - Engineering and Construction Mgmt.

Fluor's engineering and construction management expertise opened the largest hydroelectric power station in New Zealand. Manapouri Power Station, which opened in 1971, generates power by diverting the outflow of two large lakes to a powerhouse 700 feet under the earth.


Client's Challenge

For a long time, New Zealand authorities understood the power inherent in two large lakes of Southland region, Te Anau and Manapouri. Annual rainfall that is often more than 300 inches creates an overflow from the lakes averaging 13,600 cubic feet per second. Harnessing the power of that overflow would require the building of a powerhouse uniquely situated to channel the energy of both lakes.

Water would be dropped from Manapouri - including runoff from the adjacent Te Anau - through intakes and vertical sluices to a powerhouse 700 feet underground. There, it would pass through turbo-generators to create power, and then be discharged through a tailrace tunnel six miles long and thirty feet in diameter. The tunnel would carry the discharged water to Doubtful Sound, a fjord on New Zealand's southwestern coast.


Fluor's Solution

The initial contract was awarded in the summer of 1963 to Utah Construction & Mining Company, later purchased by Fluor. Project work commenced the following year with excavation work on the six-mile-long tunnel, opening an outlet channel about a half-mile long, and laying out a 13.5-mile gravel-surfaced road connecting the lake to the hydroelectric power station site.

Construction began from the fjord inward. As the shoreline was hilly and waterlogged, a former ocean liner was purchased, refitted, and docked at Doubtful Sound to provide worker accommodations.

As the tunnel was excavated inward, round-the-clock pumping operations went on to channel out water pushed into the tunnel from high pressure caused by surrounding mountains. The water's flow reached a peak of 12,000 gallons a minute.

The powerhouse at Lake Manapouri as built was enormous for an underground structure: 364 feet long, 59 feet wide, and 127 feet high. Housing seven turbines, each capable of producing 100,000 kilowatts, the powerhouse's construction required excavation work from solid rock.


Conclusion

After some 57 months, the powerhouse and the tunnel shaft from Doubtful Sound were connected. Starting ten feet underground near the powerhouse, it runs downhill for 25,000 feet before banking upward another 7,000 feet and then discharging at Doubtful Sound.

The powerhouse began producing power for New Zealand's grid after four turbo-generators were installed. The powerhouse opened in 1968.