Consents lodged for hydro power station

Consents have been lodged to build a new hydro power station on the Arnold River east of Greymouth, adding to the 90-year-old existing scheme.

The new station will generate enough electricity to power about 2000 homes, according to Manawa Energy Ltd, formed after the recent sale of Trustpower's mass market retail business.

Manawa says it wants to use flow at present being lost over the Arnold Dam. It has a design capacity of 16GW, using 30cu m a second of water, drawn from the Arnold River, which drains Lake Brunner.

The new generation facility will be next to, and below, the Arnold Dam, affecting about 250m of water. Construction will take about 20months.

The old power station will continue to operate.

As well as building a new power station — with foundations 16m underground — Manawa plans to construct a new intake channel and tailrace. It also wants to strengthen the existing dam. Consents for this have already been sought.

Greymouth Mayor Tania Gibson welcomed the announcement, saying it would boost West Coast power resilience and be good for the economy.

However, she said it was a shame Trustpower had decided last year not to go ahead with the much larger $200 million power scheme on the Arnold.

Manawa said the proposed scheme would have only minor adverse effects on the environment, against positive effects by increasing generation capacity.

That would help with long-term security of supply for the area.

The Arnold River site is highly modified, and is largely covered in exotic grasses and weeds, with some regenerating shrubs.

The only public viewpoint towards the site is from the Arnold Valley Walkway, a Department of Conservation track on the north bank of the Arnold River.

The application says the scheme has been designed to provide for fish passage.

An ecological assessment also says lamprey eels have been detected in the tailrace. However, there is uncertainty around the size of lamprey there and how many may enter the tailrace.

The aquatic ecology assessment recommends using eDNA sampling.

The existing successful fish passage pathways will continue to be available for the eels and lamprey.

An additional elver (juvenile eel) trap will be required in the new tailrace to collect elvers that become entrained in the tailrace.

The application says the construction will provide opportunities for local engineering firms and create jobs, "as well as specialists from further afield contributing to the local economy while based here for construction activities."

The Arnold River power scheme was constructed between 1929 and 1932 on a natural bend of the river. The scheme was subsequently modified in 1938 into its present configuration. — The Grey Star

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