Benmore Dam is the largest dam within the

Waitaki Waitaki District is a territorial authority district that is located in the Canterbury and Otago regions of the South Island of New Zealand. It straddles the traditional border between the two regions, the Waitaki River, and its seat is Oamaru. ...

power scheme, located in the

Canterbury Region Canterbury ( mi, Waitaha) is a region of New Zealand, located in the central-eastern South Island. The region covers an area of , making it the largest region in the country by area. It is home to a population of The region in its current f ...

of New Zealand's

South Island The South Island, also officially named , is the larger of the two major islands of New Zealand in surface area, the other being the smaller but more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman ...

. There are eight other power stations in the Waitaki Power Scheme. The dam is the largest earth-fill (zoned embankment dam) water-retaining structure in New Zealand. Its core is low permeability clay material, supported by two massive shoulders of river gravel. Lake Benmore has a volume of 1.25 billion cubic metres, about 1.5 times as much water as Wellington Harbour. The dam's spillway can cope with over 6,000 cubic metres of water per second, about 20 times the mean river flow. Benmore hydropower station 01

Benmore Power Station

With a generating capacity of , Benmore Power Station is the second largest hydro station in New Zealand behind Manapouri, and the largest dam in the country. The $62 million construction of the dam and hydroelectric station began in 1958. It was commissioned in 1965, and officially opened by Prime Minister Sir

Keith Holyoake Sir Keith Jacka Holyoake, (; 11 February 1904 – 8 December 1983) was the 26th prime minister of New Zealand, serving for a brief period in 1957 and then from 1960 to 1972, and also the 13th governor-general of New Zealand, serving from 197 ...

on 15 May that year. It was built for the

New Zealand Electricity Department The Electricity Corporation of New Zealand Ltd (ECNZ) is a New Zealand state-owned enterprise (SOE) formed on 1 April 1987, as a transition entity in the process of deregulating the New Zealand electricity market. Most of ECNZ's remaining liabil ...

; since 1999 it has been owned and operated by Meridian Energy. From 2008 to 2010 the six turbines are being refurbished at a cost of $67 million. This will enable a 6% reduction in water use for the same generation capacity, increasing annual generation by . New switchboards and an upgrade to the switchyard are also planned. Benmore is the South Island terminus of the HVDC Inter-Island link between the North and South Islands of New Zealand. The HVDC converter stations are on the west side of the tailrace, and convert 220 kV AC power to ±350 kV DC for the journey to the North Island converter station at the

Haywards Haywards is a small hillside suburb in the Hutt Valley near Wellington, New Zealand. It is notable for its large electrical substation, which is the main switching point for the Wellington region, and the home of the North Island converter stat ...

in Lower Hutt.

Otematata

Otematata is the small town that was created to support workers who constructed the dam, and their families. The town was constructed by the Ministry of Works, which residents called "Uncle Mow" or "Big Mow" as it provides every feature, including social activities and clubs, and expelled criminals from the town. After the dam was constructed, much of the village was dismantled. Many of the houses, which had been trucked in from Roxborough, were trucked away again and moved to the next site in Twizel. Today Otematata supports the dam, although with advances in technology the staffing needed to maintain the dam is drastically smaller. Due to this the town is now a small holiday community, with only around 200 permanent residents. The dam is about up the valley from the township.

Key statistics

* Lake Benmore area: ~ 75 square kilometres * Lake Benmore shoreline: 116 km * Dam crest length: 823 metres * Dam crest height: 100 metres * Dam width at base: 490 metres * Dam width at crest: 10.6 metres * Dam fill: 28 million tonnes * Head (hydraulic): 92 metres * Average river water flow: 340 m³/s * Nominal annual generation: 2,200 GWh * Installed capacity: 540 MW * Machinery: 6 x 90,000 kW vertical

Francis turbine The Francis turbine is a type of water turbine. It is an inward-flow reaction turbine that combines radial and axial flow concepts. Francis turbines are the most common water turbine in use today, and can achieve over 95% efficiency. The proc ...

s (Dominion Engineering, Canada), coupled to 6 x 90,000 kW 112,500 kVA generators (Canadian General Electric); 3 transformers totalling 1,150 MVA * Penstocks: Prestressed concrete

Transmission

Benmore is a major switching point in the New Zealand national grid and one of two major switching stations in the Waitaki Valley (the other being Twizel sub-station). The importance is largely due to the location at Benmore of the southern terminal station of the HVDC Inter-Island link. The main AC switching station is on the east bank of the tailrace, and electricity generated at Benmore Power Station is injected into the national grid here. Three major 220 kV lines containing five circuits run from the Benmore substation. Clockwise from south, they are: * A double-circuit line to the Twizel sub-station, with one circuit going via Ohau C power station and one circuit going via Ohau B power station. * A single-circuit line to Islington sub-station in

Christchurch Christchurch ( ; mi, Ōtautahi) is the largest city in the South Island of New Zealand and the seat of the Canterbury Region. Christchurch lies on the South Island's east coast, just north of Banks Peninsula on Pegasus Bay. The Avon Rive ...

, via Twizel sub-station and Tekapo B power station. * A double-circuit line to Aviemore Dam The HVDC converter stations are located on the west side of the tailrace, connected to the AC switching station by lines over the tailrace. The -350 kV thyristor Pole 2 has its valve hall on the south side of the site. A new +350 kV thyristor Pole 3 was commissioned in 2013 to replace the ageing Pole 1, and its valve hall is located adjacent to the existing Pole 2 valve hall.

References

External links

Meridian Energy
- power station information * {{Waitaki River dams Dams completed in 1965 Buildings and structures in Canterbury, New Zealand Dams in New Zealand Earth-filled dams