Bird strike, noise levels wind farm issues 

Issues of bird strike and likely noise levels from a planned wind farm north of Dunedin occupied much of the third day of an Environment Court hearing in the city yesterday.

Judge Jane Borthwick and two independent commissioners are hearing an appeal by Blueskin Energy Ltd against the Dunedin City Council’s refusal to allow the establishment of a wind farm on Porteous Hill near Warrington.

Blueskin Energy (BCL), a company formed by the Blueskin Resilient Communities Trust (BRCT), says the wind farm would benefit its own community and the rest of the country by combating climate change and providing renewable energy.

The local community would also benefit financially from the anticipated annual dividend of $100,000.But the council and many residents living close to the proposed turbine site say the adverse effects on the nearest neighbours’ enjoyment of their properties were so significant the proposal should not proceed. Many of the concerns related to anticipated noise from the wind farm, despite the number of turbines having been reduced from three 90m structures to one 110m tall turbine. The likely harm to birdlife from the huge blades was also of concern.

Avifauna expert John Craig for BCL, and Derek Onley, a witness for the opposing Blueskin Landscape and Amenity Society, disagreed about structured data relating to bird strike having to be collected at the site.

Dr Craig felt there was already ‘‘an enormous amount of useful information’’ from other New Zealand wind farms and he was happy to extrapolate data from other examples.

Mr Onley argued site-specific information was needed. Both men agreed the methodology used in relation to the retrieval of bird carcasses should be based on international best practice as used by Scottish National Heritage.

To Karen Price, representing the Porteous Hill neighbours, Dr Craig acknowledged the proposed turbine would probably kill birds. But, looking at the bird death rate from other wind farms, it would be more accurate to describe the data as carcass retrieval rate.

And when there was a single turbine, retrieval was going to be “the most thankless job in the world” unless the job was done with a dog.

Dr Craig and Mr Onley agreed the wording of any consent condition needed to be improved. Although he agreed there should be close monitoring of bird strike during the first three years of operation, Mr Onley felt it should continue “in perpetuity”.

He stood by his assessment of the need to collect statistics at the site, even when there was no activity, as there was little information in New Zealand about the effects of structures, including wind turbines, on birds. Acoustics engineer Stephen Chiles said it was almost impossible to measure sound with a constant isotropic air mass as there would always be some wind in the background.

The predicted turbine sound level at 110 Porteous Rd was 38 decibels, Dr Chiles said. That did not include any background sound.

Often, with wind farms, the turbine noise was not the loudest noise source when the wind picked up, unless a house was very close.

To determine if the wind turbine was performing as expected, other noise sources had to be removed. If there were many other sounds, it made it difficult to extract the turbine sound to see if it complied. If all the other sources were constant “it would be a breeze”, Dr Chiles said.

Background sounds in a rural area were so variable the best that could be done in measuring was to take an average over a period.

All turbines had the characteristic that their sound level increased with the increasing wind speed, then the turbine sound plateaued. While the primary objective of the background noise survey had not yet been achieved, Dr Chiles said he was happy there was enough information to assess the facts. More was needed for a condition to be formulated.

He accepted the human response to noise was highly variable and there was a strong likelihood those closest would be highly annoyed by the noise if they did not like what was producing it.

Noise perception index expert Malcolm Hunt said he had not done any detailed analysis but could say keeping the limits below 40 decibels would minimise the effect on neighbours at night. During the day, when people were out and about, he would expect more noise, he told Michael Garbett, counsel for the DCC. But, with all the turbines he had previously dealt with, he had been able to stand directly beneath the structure and have a conversation without shouting.

The noise would possibly be like that from a piece of farm machinery and the effect was likely to be intermittent. He had confidence in the data collected by the applicant, and was reasonably happy with its veracity even if the findings were based on synthetic wind data. He found nothing to suggest any bias to make the data seem better than it actually was and believed any errors were random.

The hearing continues today.