Project Aqua's impact unknown, says expert

No one really knows how Project Aqua will affect the Waitaki River, Canterbury University expert Tim Davies says.

Dr Davies told a public meeting organised by anti-Project Aqua group Waitaki First in Oamaru it was impossible to say at this stage what the scheme's impact would be.

Dr Davies said the one thing that seemed "quite clear" was that the Waitaki would become less braided with a lower flow. It is proposed to drop from the average present flow of about 370 cubic metres a second (cumecs) to 120.

The National Institute of Water and Atmospheric Research has predicted that the amount of sediment carried would be reduced by 70 to 90 per cent every year, and Dr Davies said he suspected it could be greater.

That would mean less material being deposited along the coast, causing cliff erosion of maybe a metre a year. The outcome for the lagoon at the river mouth was not known.

Meridian plans to send 450-cumec "flushing flows" down the river for 24 hours every five to seven weeks to clear out sediment. But possible errors in sediment flow predictions meant the flushes might not work, Dr Davies said.

"It's one of the things I've got the most concerns about. There's some doubt as to what flows might be required and for what time period.

"It's very difficult to calculate flushing effect accurately. It might cost Meridian considerably more water than it contemplated."

Dr Davies described Meridian's "optimised" flow scenarios as unreliable and unrealistic, based on an assumption of perfect weather forecasts. There was no way it could prevent major floods like the one in 1995; it would have to "react after the event".

Other matters that he said needed more attention were the possibility of sudden severe bank erosion and bridge pier scouring during floods, and the design of the places where the canal crossed tributaries flowing into the river.

Natural History New Zealand documentary researcher and producer Rod Morris said braided rivers such as the Waitaki were "one of the worst habitats in the world to put a hydro scheme on".

He urged everyone to value the tiny native animals that had adapted to survive in the braided Waitaki. Among them are chunky camouflaged grasshoppers, geckos that date back to Gondwanaland, alpine cicadas, and the "extraordinarily rare" long jaw galaxiids that have been isolated from any other genetic input for at least 35 million years.

The Waitaki is also home to the wrybill - the only bird in the world with a laterally curved beak for trimming food off the underside of rounded river rocks - the endangered black stilt, and the rare black-fronted tern and black-billed gull.

NZ had probably the world's third best set of broad braided rivers, he said.

The best was in North America and the second at the foothills of the Himalayas. "They're very, very rare environments."

Mr Morris said hydro schemes provided solutions for a terrifically short time, destroying "stuff that's been around for millions of years".

The Canterbury Plains had been built up by gravels and sediment from braided rivers over the past two million years.

Translucent crustaceans less than 2.5cm long were being found living metres below the plains.

"There are at least 20 species. Most are not even described yet."

The Waitaki had already been damaged by hydro developments, "but that's not an excuse for destroying the habitat even further", he said.

Meridian said last month that it was committed to ensuring Project Aqua did not harm native wildlife.

It would do all it could to help threatened and endangered species and aimed to maintain the lower Waitaki's biodiversity, spokesman Alan Seay said.

Fish and bird species would be monitored and action taken if their populations were shown to be suffering.

Project Aqua

* $1.2 billion energy scheme on the Lower Waitaki River.

* The Meridian Energy project involves diverting up to 73 per cent of the North Otago river through six power stations along a 60km hydro canal.

- NZPA