The Manapouri Power Station is the largest hydro power station in New Zealand.
The underground station is owned and operated by Meridian Energy. It lies deep in a remote area of New Zealand’s South Island on the western arm of Lake Manapouri, in Fiordland National Park.
- Water flows from Lake Te Anau down the upper Waiau River to Lake Manapouri.
- Water is 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.
- Water from Lake Manapouri is used to generate electricity at the underground West Arm power station.
- The tailwater discharge from the power station is released into Deep Cove in Doubtful Sound.
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 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.
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, far short of the designed peak capacity of 700 MW. Construction of a second tailrace tunnel, 10 km long and 10 metres in diameter, finally solved the problem. The increased exit flow also increased the effective head, allowing the turbines to generate more power without using more water.
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|