View source for Benmore Dam

{{Short description|Dam in New Zealand}}
{{Use New Zealand English|date=April 2024}}
{{Infobox dam
| name                 = Benmore Dam
| image                = Benmore_Dam.jpg
| image_caption        = 
| name_official        = 
| location             = [[Canterbury Region]], New Zealand
| location_map         = New Zealand
| location_map_caption = 
| location_map_size    = 
| coordinates          = {{coord|44|33|50.92|S|170|11|49.92|E|type:landmark|display=inline,title}}
| dam_crosses          = [[Waitaki River]]
| dam_type             = Earth-filled dam
| dam_length           = {{convert|823|m|abbr=on}}
| dam_height           = {{convert|110|m|abbr=on}}
| dam_width_base       = {{convert|490|m|abbr=on}}
| dam_width_crest      = {{convert|10.6|m|abbr=on}}
| dam_volume           = 28&nbsp;million&nbsp;tonnes
| spillway_type        = 
| spillway_capacity    = {{convert|3400|km3|abbr=on}}
| construction_began   = 
| opening              = 
| demolished           = 
| cost                 = $62&nbsp;million
| owner                = 
| res_name             = [[Lake Benmore]]
| res_capacity_total   = {{convert|1.25|km3|acre feet|abbr=on}}
| res_catchment        = 
| res_surface          = {{convert|75|km2|abbr=on}}
| res_max_depth        = {{convert|102|m|abbr=on}}
| plant_operator       = [[Meridian Energy]]
| plant_hydraulic_head = {{convert|92|m|abbr=on}}
| plant_turbines       = 6 x {{convert|90|MW|abbr=on}}
| plant_capacity       = {{convert|540|MW|abbr=on}}
| plant_annual_gen     = {{convert|2,215|GWh|abbr=on}}
| plant_type           = 
| plant_commission     = 1965
| plant_decommission   = 
| website              = 
| extra                = 
}}

'''Benmore Dam''' is the largest dam within the [[Waitaki River|Waitaki]] [[hydroelectricity|power scheme]], located in the [[Canterbury Region]] of New Zealand's [[South Island]].  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&nbsp;cubic metres of water per second, about 20&nbsp;times the mean river flow.
[[File:Benmore hydropower station 01.jpg|thumb|260px|Dam of Benmore hydropower station]]
[[File:Benmore hydropower station 02.jpg|thumb|260px|Lake below Benmore hydropower station]]

==Benmore Power Station==
With a generating capacity of  {{convert|540|MW}}, Benmore Power Station is the second largest <ref>{{Cite web|url=https://www.meridianenergy.co.nz/about-us/our-power-stations/hydro/benmore|title = Benmore dam hydro station}}</ref> hydro station in New Zealand behind [[Manapouri Power Station|Manapouri]], and the largest dam in the country.

Construction of the dam and hydroelectric station began in 1958 at a cost of $62 million. It was commissioned in 1965, and was officially opened by Prime Minister Sir [[Keith Holyoake]] on 15 May that year.<ref name=ODT_rebuild>{{cite web|url=http://www.odt.co.nz/the-regions/north-otago/29502/benmore-gets-more-with-first-full-rebuild|title=Benmore gets more with first full rebuild|last=Bruce|first=David |date=30 October 2008|work=[[Otago Daily Times]]|accessdate=2008-10-30}}</ref> It was built for the [[New Zealand Electricity Department]]; since 1999 it has been owned and operated by [[Meridian Energy]].<ref name=ODT_rebuild/>

From 2008 to 2010, the six turbines were refurbished at a cost of $67 million. This enabled a 6% reduction in water use for the same generation capacity, increasing annual generation by {{convert|70|GWh|abbr=on}}. New switchboards and an upgrade to the switchyard were also undertaken.<ref name=ODT_rebuild/>

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&nbsp;kV AC power to ±350&nbsp;kV DC for the {{convert|610|km|abbr=on}} journey to the North Island converter station at the [[Haywards]] 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 [[Roxburgh, New Zealand|Roxburgh]], were trucked away again and moved to the next site in [[Twizel]].<ref>{{Cite web|url=https://www.rnz.co.nz/national/programmes/spectrum/audio/201753844/power-for-the-people|title=Power for the People|date=2015-05-11|website=[[RNZ]] |language=en-nz|access-date=2020-02-09}}</ref>

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 {{convert|8|km}} up the valley from the township.

==Key statistics==
* Lake Benmore area: ~ 75 square kilometres
* Lake Benmore shoreline: 116&nbsp;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&nbsp;kW vertical [[Francis turbine]]s (Dominion Engineering, Canada), coupled to 6 x 90,000&nbsp;kW 112,500 kVA [[Electrical generator|generators]] (Canadian General Electric); 3 transformers totalling 1,150 MVA
* Penstocks: Prestressed concrete

{{wide image|Benmore Dam Pano (22-03-08).jpg|700px|Benmore Dam from the south lookout, near the [[spillway]]}}

==Transmission==
{{main| HVDC Inter-Island}}
Benmore is a major switching point in the New Zealand [[National Grid (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&nbsp;kV lines containing five circuits run from the Benmore substation. Clockwise from south, they are:<ref>{{cite web| url=https://www.transpower.co.nz/system-operator/key-documents/maps-and-diagrams| title=Maps and Diagrams| publisher=Transpower New Zealand| accessdate=18 July 2017| archive-date=10 June 2017| archive-url=https://web.archive.org/web/20170610215538/https://www.transpower.co.nz/system-operator/key-documents/maps-and-diagrams| url-status=dead}}</ref>
* A double-circuit line to the Twizel sub-station, with one circuit going via [[Ōhau C]] power station and one circuit going via [[Ōhau B]] power station.
* A single-circuit line to Islington sub-station in [[Christchurch]], 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&nbsp;kV thyristor Pole 2 has its valve hall on the south side of the site. A new +350&nbsp;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.

==See also==
{{stack|{{Portal|New Zealand|Water|Renewable energy}}}}
*[[National Grid (New Zealand)]]
*[[List of power stations in New Zealand]]
*[[Electricity sector in New Zealand]]
*[[New Zealand electricity market]]

==References==
{{reflist}}

==Further reading==
*{{cite book | editor=Martin, John E | title=People, Power and Power Stations| location=Wellington| publisher=Bridget Williams Books Ltd and Electricity Corporation of New Zealand| year=1991 | isbn=0-908912-16-1| pages = 316 pages}}
* {{cite book | author=Reilly, Helen | title= Connecting the Country – New Zealand's National Grid 1886 - 2007| location=Wellington| publisher=Steele Roberts| year=2008 | isbn=978-1-877448-40-9| pages = 376 pages}}
* {{cite book | author=Sheridan, Marion | title=Dam Dwellers – End of an Era| location=Twizel| publisher=Sheridan Press| year=1995 | isbn=0-473-03402-6| pages = 392 pages}}
*Power for the People (2015) Spectrum for RNZ. 24 minutes. Available at [https://www.rnz.co.nz/national/programmes/spectrum/audio/201753844/power-for-the-people RNZ].

==External links==
*[https://web.archive.org/web/20150612111124/https://www.meridianenergy.co.nz/about-us/benmore-hydro-station/ Meridian Energy] - power station information
* {{commons category-inline}}
{{Meridian Energy|state=autocollapse}}
{{waitaki}}
{{Waitaki River dams}}

[[Category:Dams completed in 1965]]
[[Category:Buildings and structures in the Canterbury Region]]
[[Category:Dams in New Zealand]]
[[Category:Earth-filled dams]]