Scheme 'to power 47,000 homes'

TrustPower's proposed Wairau power scheme would generate enough electricity to supply 47,000 homes, the Environment Court panel considering whether the company should be granted resource consent for the project has been told.

The Environment Court reconvenes next Monday, having taken a break while Judge Gordon Whiting and commissioners Helen Beaumont, Alex Sutherland and John Mills took a familiarisation tour of the Wairau River and read volumes of expert evidence.

The proposed power scheme would generate an additional 367 gigawatt hours of electricity a year, the panel was told when the hearing began on November 3.

TrustPower engineering manager Peter Lilley, Tonkin & Taylor director Robin Dawson and Beca Infrastructure technical director Graham Levy opened the hearing with an overview of the $280 million scheme, which would divert water from the Wairau through 47 kilometres of canals and five power stations.

Designs were at the concept stage and accurate to about 10-20 metres, they said.

Local supply currently met 16 per cent of demand, the court was told. With no new supply, this would fall to less than 10 per cent by 2025.

Mr Dawson said the Wairau River fell 253m between the scheme intake 2km above the Branch confluence and the outfall at Marchburn.

Up to 40 cubic metres of water per second (cumecs) would be taken from the river at the intake, with 35 cumecs going into the scheme and 5 cumecs available for sediment flushing and fish passage, the court was told.

Depending on the season and ecological requirements, the Wairau would retain 10-20 cumecs of flow.

The scheme would be shut down in a flood or if flows were unusually low.

This was a small-steps "cascade" system with no large dams but with seven hours of inbuilt storage to meet demand at peak times, the court was told. When river flows were very low, water could be progressively held then released through the scheme with stations pulsing in sequence.

This was essentially an extension of the existing Branch hydro scheme, said Messrs Lilley, Dawson and Levy.

The new and Branch canals would meet at the headpond above the existing Wairau power station, where an additional station would be built alongside the old.

A new 15-hectare regulation pond below the Wairau stations would fill and empty twice a day. This would have a ponded "moat" around the edge to be developed as a wetland.

Each of the scheme's next four power stations would be fed by 7-9km stretches of canal widening at the end into a headpond, to generate 6.7 to 12.6MW of electricity.

The canal feeding power station five, which was designed to generate 22.3MW, would be three times the length of earlier sections and would be divided in three so sections could be isolated in an emergency.

Earthquakes and floods were the main threats to the scheme, the panel was told. To avoid major breaches, canals would be cut low into the land.

In heavy rainfall and if a section had to be shut down and drained, water could be removed via spillways. Open flumes, culverts and buried pipelines would carry the scheme where it crossed 38 tributaries of the Wairau and State Highway 63 in two places.

Eight local catchments would be collected along the way.

Recreational areas at the headpond and the tailrace would include a kayaking playhole, boat-launching facilities, toilets and parking.

TrustPower would also legally protect 18.7ha of ecologically significant scrub and forest as well as 15.5ha of exotic forest, which would be gradually replaced with native plants. Ten hectares of wetland and shrubland would be planted and a 10m strip where Saltwater Creek met the canal below the Wairau Power Station would be encouraged to regenerate.

- The Marlborough Express