Manapouri Power Station is an underground hydroelectric power station owned and operated by Meridian Energy Limited, and is the largest hydroelectric power station in New Zealand. It lies deep in a remote area of New Zealand's South Island on the western arm of Lake Manapouri, in Fiordland National Park. Most (~610 MW) 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 southeast.
The construction of the station was a massive feat of civil engineering. The majority of the station, including the machine hall and two 10-km tailrace tunnels, was excavated under a mountain. During the 1960s, environmental protests against its construction, which resulted in the planned raising of lake levels, galvanised New Zealanders, and was considered one of the starting points of New Zealand environmentalism. The campaign to prevent the lake from being raised involved politicians and senior bureaucrats and succeeded in modifying the original plans, permitting the construction of the power station. This also prevented it from operating to the full degree that had originally been intended.
The power station is housed in a cavern excavated from solid granite rock 200 metres below the surface 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.
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.
See Save Manapouri Campaign.
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.
- February 1963, Bechtel Pacific Corporation won the design and supervision contract.
- 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.
- August 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.
- February 1964, tailrace-tunnel construction began.
- December 1967, powerhouse construction was completed.
- October 1968, tunnel breakthrough.
- 14 September 1969, the first water flowed through the power station.
- September/October 1969, commissioning of the first four generators.
- August/September 1971, the remaining three generators were commissioned.
- 1972, the station was commissioned. It was then that engineers confirmed the limitations of peak capacity due to excess friction in the tailrace tunnel.
- June 1997, construction work by a Dillingham Construction / Fletcher Construction / Ilbau joint venture began on the second tailrace tunnel.
- 1998, the Robbins tunnel boring machine starts drilling at the Deep Cove end of the tunnel.
- 2001, tunnel breakthrough.
- 2002, the second tunnel was commissioned. 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. As of June 2006, four generating units have been upgraded, and the project was on schedule for completion in August 2007.
- July 1956, the New Zealand Electricity Department announced the possibility of a project using the Manapouri water, an underground power station and underground tailrace tunnel discharging the water at Deep Cove in Doubtful Sound. Five months later, Consolidated Zinc Proprietary Limited formally approached the New Zealand government about acquiring a large amount of electricity for aluminium smelting.
- 19 January 1960, the Labour Government and Consolidated Zinc signed a formal agreement for Consolidated Zinc to build both an aluminium smelter at Tiwai Point and a power station in Manapouri. The agreement violated the National Parks Act, which provided for formal protection of the Park, and required subsequent legislation to validate the development. Consolidated Zinc received exclusive rights to the waters of both Lakes Manapouri and Te Anau for 99 years. Consolidated Zinc planned to build dams that would raise Lake Manapouri by 30 metres, and merge the two lakes. The Save Manapouri Campaign was born, marking the beginning of the modern New Zealand environmental movement.
- 1963, Consolidated Zinc decided it could not afford to build the power station. The New Zealand government takes over. Electricity generated by the plant is sold to Consolidated Zinc at basement prices, with no provision for inflation.
- 1969, Consolidated Zinc's electric power rights were transferred to Comalco Power (NZ) Ltd, a subsidiary of the Australian-based Comalco Industries Pty Ltd.
- 1970, the Save Manapouri petition to the government attracted 264,907 signatures.
- 1972, New Zealand elected a new Labour government.
- 1973, the Prime Minister, Norman Kirk, honoured his party’s election pledge not to raise the levels of the lakes. He created an independent body, the Guardians of Lake Manapouri, Monowai, and Te Anau to oversee management of the lake levels. The six Guardians were all prominent leaders of the Save Manapouri Campaign.
- 1984, the Labour Party returned to power in the general election. The resulting period was tumultuous, with Labour's controversial ministers Roger Douglas and Richard Prebble driving rogernomics, a rapid introduction of "free market" reforms and privatisation of government assets. Many suspected the Manapouri Powerstation would be sold, and Comalco was the obvious buyer.
- 1991, the Save Manapouri Campaign was revived, with many of the same leaders and renamed Power For Our Future. The Campaign opposed selling off the power station to ensure that Comalco did not rehabilitate its plans to raise Lake Manapouri's waters. The Campaign was successful. The government announced that Manapouri would not be sold to Comalco.
- 1 April 1999, ownership of the Manapouri power station was transferred from the Electricity Corporation of New Zealand to Meridian Energy Limited.
Specifications and statistics
| Average annual energy output
|| 4800 GW·h |
| Station generating output
|| 850 MW |
| Number of generating units
|| 7 |
| Net head
|| 166 m |
| Maximum tailrace discharge
|| 510 m³/s |
|| 7 × vertical Francis type, 250 rpm |
|| 7 × 13.8 kV, 121.5 MW / 135 MVA |
|| 7 × 13.8 kV/220 kV, rated at 135 MVA |
| Machine hall
|| 111 m length, 18 m width, 34 m height |
| First tailrace tunnel
|| 9817 m, 9.2 m diameter |
| Second tailrace tunnel
|| 9829 m, 10.05 m diameter |
| Road access tunnel
|| 2040 m, 6.7 m wide |
| Cable shafts
|| 7 × 1.83 m diameter, 239 m deep. |
| Lift shaft
|| 193 m |
|| 7 × 180 m long |