Lake Onslow

Lake Onslow is a man-made lake east of Roxburgh and south of Alexandra in the Otago region of New Zealand. It lies 700 m (2,300 ft) above sea level. It was formed in 1890 by the damming of the Teviot River and Dismal Swamp, with a new dam built in 1982 that raised the lake level by 5 m (16 ft). It is the site considered for a pumped-storage hydroelectricity project.

"Onslow PHS" redirects here. For other uses, see Pumped-storage hydroelectricity.

Lake Onslow
Lake Onslow In May 2014
Lake Onslow In May 2014
Location of Lake Onslow
Location of Lake Onslow
Lake Onslow
LocationOtago, South Island
Coordinates45°33′S 169°37′E
Typereservoir
Primary inflowsTeviot River
Primary outflowsTeviot River
Basin countriesNew Zealand
Surface elevation700 m (2,300 ft)

History

Lake Onslow first formed in 1890 when a dam was built that flooded the Dismal Swamp; the Teviot River flowed through the swamp. The water from this lake was used for mining, irrigation and hydroelectricity. In 1982, a new and higher dam was built that raised the lake level by 5 m (16 ft); the old dam is now drowned.[1] The water usage rights jointly sit with Pioneer Energy (formerly the Otago Central Electric Power Board) and the Teviot Irrigation Company.[2]

In 2019, the Interim Climate Change Committee proposed that the lake be used for a pumped hydro-storage system to provide backup electricity generation in dry years. The project had first been considered by hydrologist Earl Bardsley of the University of Waikato since 2002 and proposed in 2005.[3][4][5] In July 2020, Minister of Energy Megan Woods announced that the New Zealand government would fund a detailed feasibility study of the plan.[6] If progressed, the scheme would be the biggest infrastructure project in New Zealand since the 1980s, employ an estimated 3500 to 4500 people, and take four to five years to build and a further two years to fill.[7] One option could be 5 TWh of storage and a 1.2 GW power station, equivalent to half a year of full production.[8]

If the project goes ahead it will completely drown and submerge a small scroll plain with its swirling and migrating meanders (formerly known as Dismal Swamp). The scroll plain is a miniature example of the nearby Taieri Scroll Plains[9] and has formed because of the low and decreasing gradient of the stream valley due to slow progressive tectonic back-tilting of the catchment.[10]

In March 2023 the government estimated the cost of the storage project at $15.7 billion.[11]

References
  1. "Our history". Pioneer Energy. Retrieved 16 May 2022.
  2. Morgan, Jared (1 August 2020). "Lake Onslow project: area has seesawing history". Otago Daily Times. Retrieved 16 May 2022.
  3. O'Connor, Rose (16 May 2022). "Pumped storage: A game-changer for New Zealand's electricity needs?". Stuff. Retrieved 16 May 2022.
  4. "Accelerated electrification: Evidence, analysis and recommendations" (PDF). Interim Climate Change Committee. 30 April 2019. pp. 67–68. Retrieved 16 July 2019.
  5. Jones, Pam (18 September 2019). "Massive hydro storage plan to be reassessed". Otago Daily Times. Retrieved 18 September 2019.
  6. "Central Otago hydro project could be 'game changer'". Otago Daily Times. 26 July 2020. Retrieved 26 July 2020.
  7. Thomas Coughlan (26 July 2020). "Government wants 100 per cent green electricity by adding 'battery' power to hydro power". Stuff. Retrieved 26 July 2020.
  8. "Does New Zealand's plan for a nation-sized battery hold water?". RenewEconomy. 15 October 2020.
  9. "Upper Taieri Wetlands Complex". Otago Regional Council. 12 April 2022. Retrieved 16 May 2022.
  10. Hayward, Bruce W (March 2022). "Lake Onslow's small scroll plain, Otago". Geoscience Society of New Zealand Newsletter (36): 22–25.
  11. Marc Daalder (16 March 2023). "Lake Onslow scheme to cost $15.7 billion". Newsroom. Retrieved 16 March 2023.
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