Oamaru, June 29 NZPA - A new hydro scheme on the lower Waitaki River would save the habitat of endangered river bird species, the Environment Court was told today.

Meridian Energy wants to take water from Lake Waitaki and pass it through a tunnel and power station before discharging the water into the Waitaki River at Stonewall. It has been granted resource consent to take the water, but that decision has been appealed by the Lower Waitaki River Management Society.

The hearing began in Oamaru last week, with interested parties and a panel of four Environment Court commissioners seeking clarification and challenging claims made by Meridian's witnesses.

The written evidence of Boffa Miskell senior ecologist Mark Sanders was cross-examined today.

His evidence centred on the impact of the $900 million North Bank Tunnel Concept (NBTC) on the area's braided river birds.

He said the loss of habitation being experienced due to increased vegetation would be controlled under the scheme.

Increased riverbed vegetation control would also reduce weed encroachment, improving the river's ecological condition.

He said under the status quo, the habitat was becoming scarce due to vegetation encroachment and the resulting reduction of bare gravels and islands.

"This would be detrimental because the extensive weed cover on the Waitaki River is likely to be a limiting factor for birds," he said.

The evidence was questioned by counsel for the Lower Waitaki River Management Society, Camilla Owen.

"My concern is that Meridian is not required to manage the population size (of the birds)," Miss Owen said.

"The NBTC ... is putting extra pressure on these species. Is that not a concern from a conservation perspective?"

Dr Sanders disagreed, saying the situation would be improved.

"In my view, if the NBTC proceeds ... the various management plans will make the situation better, in particular with increased availability of riverbed habitat. This is a positive thing."

Mrs Owen asked why a more comprehensive assessment of breeding habitats in the area had not been formulated, to which Dr Sanders replied it was too early, as the mooted date for the scheme was 2016.

"It is not necessary to know now, it is necessary to know what's available immediately prior to commission," he said.

"The closer to the time, the better."

Another undertaking of the proposal would be the development of management islands.

Dr Sanders said birds on the islands would be less prone to predators and less vulnerable to disturbance and trampling by stock, dogs, and humans on foot or in four-wheel-drive vehicles.

A trial management island carried out last year was used by a more diverse and abundant number of birds than an adjacent site, he said.

"This demonstrates that the habitat enhancement proposed in the draft Braided River Bird Management Plan is operationally feasible, and can provide suitable habitat essentially immediately."

However, only a small number of older chicks or fledglings were found later in the season due to predators, he said.

The hearing continues in Oamaru tomorrow and will move to Christchurch next Monday.