The Manapouri Power Station is the largest hydro power station in New Zealand with a maximum output of 800 megawatts. In a year it produces enough energy for about 619,000 average New Zealand homes – which is more than 1/3rd of the number of homes in NZ (as at end of 2014). But the power station was really built to provide power for NZAS – a significant proportion of the station’s power output is consumed by an aluminium smelter operated by New Zealand Aluminium Smelters Limited (NZAS) at Tiwai Point near Bluff, some 160 km to the south-east.
The underground station is owned and operated by Meridian Energy.
As you can see, the Manapouri Power Station is located at the end of the West Arm of Lake Manapouri which is in the Fiordland National Park (google maps, wikipedia, or DOC). And Fiordland is part of the Te Wahipounamu – South West New Zealand World Heritage Area (wikipedia).
The water comes from Lake Manapouri, Lake Te Anau via the Waiau River (into Lake Manapouri), and also diverted from the Mararoa River, at the Manapouri lake control structure, into Lake Manapouri (except during times when the water is turbid or highly coloured when it is discharged down the lower Waiau River).
After dropping down the vertical penstocks, the water enters the Machine Hall and the turbines to generate electricity. The water discharges from the power station into the tailrace tunnel and is released into Deep Cove in Doubtful Sound – 10 kilometres away (in a straight line north-west from the power station).
- The power station is housed in a cavern (111 meters long, 18 meters wide, 39 meters high) excavated from solid granite rock 200 metres below the surface of Lake Manapouri.
- Access to the power station is via a two-kilometre vehicle-access tunnel which spirals down (1-in-10 gradient) from the surface and is wide enough for vehicles to pass. Alternatively people can reach the powerhouse by an elevator which descends 220 meters (equivalent to a 70-story building) – a journey that takes two-and-a-half minutes.
- The power station uses a 178 meter height difference between Lake Manapouri and the sea at Deep Cove.
- Two tailrace tunnels take the water that passes through the power station to Deep Cove, a branch of Doubtful Sound, 10 km away. The station was originally built with only one tailrace tunnel, but a second tunnel was commissioned in 2002.
- 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.
In the original power station project there were 16 fatal accidents on the job. In looking and marvelling at the construction, we cannot ignore their deaths. It is a reminder of the dangers these people faced daily.
The first surveyors mapping out this corner of New Zealand noted the potential for hydro generation in the 178-metre drop from the lake to the Tasman Sea at Doubtful Sound. The idea of building a power station was first suggested in 1904, but the remoteness of the location and the scale of the engineering task made any project infeasible at the time.
In 1926, the New Zealand Sounds Hydro-Electric Concessions Company obtained water rights from the government to implement a scheme to use power from Manapouri to produce fertilizer and munitions. The idea was to use electricity to fix nitrogen from the atmosphere. The scheme did not proceed and the water rights lapsed.
In 1955 the modern history of Manapouri starts, when a geologist with Consolidated Zinc Proprietary Ltd identified a commercial deposit of bauxite in Australia on the west coast of Cape York Peninsula, near Weipa. It turned out to be the largest deposit of bauxite in the world yet discovered. In 1956 The Commonwealth Aluminium Corporation Pty Ltd, later known as Comalco, was formed to develop the bauxite deposits. The company started investigating sources of large quantities of cheap electricity needed to reduce the alumina recovered from the bauxite into aluminium. Comalco settled on Manapouri as that source of power and Bluff as the site of the smelter. The plan was to refine the bauxite to alumina in Queensland, ship the alumina to New Zealand for smelting into metal, then ship it away to market.
- 1904 Potential for a hydro scheme first recognised by Mr P S Hay, of Public Works Department
- 1927 Public Works Department survey parties investigate the area
- 1947 Aluminium Co of Canada examines water resources
- 1954 Ministry of Works reports on various possible schemes
- 1955 Building restrictions on Crown Land within 100 feet (30m) of average water level of Lake Manapouri
- 1959 NZ Government invites Consolidated Zinc to consider hydro-electric potential of Lakes Manapouri and Te Anau
- 1960 Consolidated Zinc Prop. Ltd. granted rights to develop power from Manapouri/Te Anau lakes, Waiau and Mararoa rivers.
- 1960 Petition of 25,000 signatures against raising of Lake Manapouri
- 1960 Manapouri Development Validity Act enacted
- 1961 Bechtel Corporation’s investigations for Consolidated Zinc begin
- 1961 Power station site reached by vertical tunnel
- Apr 1962 Work and investigation suspended
- Jan 1963 Government to build power station
- Feb 1963 Bechtel instructed by Ministry of Works to start construction
- July 1963 Utah Construction and Mining Company and two local firms won contracts to construct the tailrace tunnel and Wilmot Pass road. Utah Construction also won the powerhouse contract.
- Aug 1963 Manapouri – Te Anau Development Act enacted
- 29 Aug 1963 The Wanganella, a former passenger liner, was moored in Doubtful Sound to be used as a hostel for workers building the tailrace tunnel. During the 1930s she was a top-rated trans-Tasman passenger liner, with accommodation for 304 first-class passengers. She continued to serve as a hostel until December 1969.
- Sept 1963 Wilmot Pass Road commenced
- 4 Feb 1964 First shot fired on Tailrace Tunnel
- 1 Nov 1965 Wilmot Pass Road completed
- 1966 1963 Act amended to let Crown take more power from Manapouri for National Grid
- June 1966 Transmission Line started
- July 1966 Manapouri controlled level 610ft (185.9m) ASL 27.5 ft (8.4m) above natural mean level
- 1967 Pilot shoreline clearing carried out
- Dec 1967 powerhouse construction was completed
- 5:42am 22 Oct 1968 Tailrace Tunnel hole through
- 29 Aug 1969 Work on Tailrace Tunnel completed
- 6 Sep 1969 Tunnel filled with water
- 14 Sep 1969 First power transmission
- 29 Sep 1969 Second machine commissioned
- 16 Oct 1969 Third machine commissioned
- 30 Oct 1969 Fourth machine commissioned
- 17 Apr 1970 Wanganella leaves Deep Cove for Hong Kong
- Dec 1970 Second petition of 264,900 signatures presented
- Apr 1971 First aluminium smelted at Tiwai Point
- Aug/Sept 1971 The remaining three generators were commissioned
- Sept 1971 Power Station complete
- Feb 1972 Te Anau Lake Control started
- 28 Apr 1972 Transmission lines completed
- July 1972 Manapouri Lake control started
- 10 Feb 1973 Guardians of the Lake established
- Apr 1974 Te Anau outlet into Waiau river diverted
- Nov 1975 Manapouri to be operated within natural levels
- 17 Sep 1977 Guardians of the Lake Guidelines announced
- 22 Dec 1977 Government endorses the Guardians’ guidelines
- 10 Dec 1997 Second Tailrace Tunnel given go-ahead
- 9 Jun 1997 First blast of construction at West Arm, construction work by a Dillingham Construction / Fletcher Construction / Ilbau joint venture
- 23 Sep 1997 First blast of construction at Deep Cove
- 10 Apr 1998 Tunnel Boring Machine (TBM) arrives at Deep Cove
- 12 Jun 1998 until 13 Mar 2001 Work continues 24 hours a day, seven days a week
- 12 May 2001 TBM demobilisation completed
- 5 May 2002 Tunnel 2 fully operational
- 2002 – 2008 A $98 million mid-life refurbishment of the seven generating units begins, with the goal of raising their eventual output to 135 MVA (121.5 MW) each