Manapouri Underground Power Station

A major engineering achievement the Manapouri Underground Power Station, at West Arm, is unique in that nearly all of it is built underground.

The main customer for the power produced at Manapouri is the Tiwai Aluminium smelter near Bluff for which the power station was constructed by the New Zealand Government.
Manapouri Power station had a long history and was built only after considerable controversy.

A detailed report on the country's hydro-electric potential was prepared in 1904 by P S Hay and was presented to Parliament appended to the Public Works Statement.Hay's report as well as being very thorough, was to some degree prophetic.He pointed out that to develop the waters of Te Anau and Lake Manapouri to their full extent, the water from both lakes would have to be diverted into the Sounds.He said,

"It is not likely for scenic reasons that a high dam would be built at Manapouri. The present beauty of the lake is worth preserving to the fullest extent"
and .. "These two schemes will likely remain as reserves until all the smaller schemes are exhausted. It may happen that a great part of the power would be used at the power station in the Sounds, in electro-chemical and electro-metallurgical work. The possession of such enormous possible hydraulic-power schemes at the seashore, with deep-water access, is, as far as I know unique.
This may lead to their utilization, at no very distant date, for industries now non-existent."

In 1960, no sooner had the government signed an agreement with Comalco giving it the right to raise the level of both Lakes Manapouri and Te Anau than it was the subject of a petition to Parliament sponsored by the Forest and Bird Protection Society. This petition which had over 250,000 signatures was only the opening shot in a battle that went on for a decade and a half.
In 1973 the new government of Norman Kirk agreed not to raise the lake level.
Eventually construction of the power station was carried out by the Government and it was commissioned in 1969.
The Tiwai Point smelter produced its first aluminium in April 1971 but it was not until 1975 that both political parties agreed not to operate the two Lakes outside their natural limits and not until December 1979 that the Government was actually relieved of its obligation to raise the level of Lake Manapouri'

The Manapouri issue was an early manifestation of the increase in concern for the "environment" that came in New Zealand and elsewhere in the world with the prosperity of the sixties. This concern was multi-faceted; it related to the destruction of forests, the cleanliness of air and water, and to the over-exploitation of finite resources as well as to the growth of technological society and the lifestyle this was seen to impose.

A commercial tour to the Manapouri Underground Power Station Excursion takes 4 hours by launch across the lake to West Arm, then travel by coach down a 2km tunnel, seemingly into the bowels of the earth. It’s an exciting and interesting trip, but not for the claustrophobic, as the coach appears to be only centimetres from the granite walls. On arrival in the huge machine hall, you learn how the lake’s waters are diverted through vertical penstocks to turbines in the powerhouse 213m below the ground. From here the water is discharged by way of a 10km tailrace into Deep Cove on Doubtful Sound.