Rudman's city: Noisy noise barrier win creates more problems

By BRIAN RUDMAN

Opponents of the $300,000 noisy noise barrier alongside the regional botanic gardens at Manurewa are firing up their gas axes in preparation for the demolition party. This follows the Manukau City Council's vote last Thursday supporting their call for its destruction.

For the protesters it was a great victory, leaving the parks committee of the Auckland Regional Council, which meets this Thursday to decide what happens next, little room to move. Though the ARC staff still have hopes of a win-win solution emerging, somehow it's hard to see that happening.

By siding with its protesting citizens, the city council has signalled, in effect, that anything short of capitulation by the ARC, whose wall it is, is likely to lead to a lengthy and expensive Resource Management Act battle between the two councils.

A win-win solution would, of course, have been the ideal solution - one where the new peace and quiet of the adjacent bush garden was matched by the protesters regaining the quality of life they previously enjoyed.

The problem is there is no common ground about what quality of life did exist beforehand. Neither is there any agreement about the wall's effect.

I've already noted that the quality of life at the Southern Motorway boundary of the complainants' homes seemed hellish to me, metal wall across the motorway or not.

The noise at the bottom of their gardens was averaging 73 decibels (dBA) between 3.30 pm and 4.30 pm, with peaks reaching 95dBA. If these levels of sound had come from your stereo, you would have the noise police storming in to confiscate your equipment.

It was this continous deafening noise that lead the botanic gardens to erect its wall, so that visitors could better commune with nature - or, more to the point, hear a guide describe the plants.

The shiny 3.5m by 440m steel wall went up in January, after a non-notified application to Manukau City, and soon the complaints from across the motorway came flooding in. The noise was bouncing off the new wall, back into homes across the way. Some claimed the motorway noise was louder. Some who had not been affected in the past said they now were. Others noted a different pattern of sound.

It wasn't just the odd crank, the objections were in the dozens. So off went the ARC and the MCC to seek a solution. Almost a year on, they're still looking.

The big problem for the bureaucrats and the politicians is that they're seeking a solution to a problem that their acoustic advisers, Marshall Day Acoustics, say does not exist. In December 1999, well before the wall went up, partner Keith Ballagh advised that any reflection across the motorway from such a wall would be 0.7dBA. He said, "We do not think this would be an appreciable increase as it normally requires a 3dBA change in noise level to be noticeable under normal conditions. Thus in our opinion there would be no noticeable acoustic effect for dwellings on the opposite side of the motorway".

Partner Chris Day says before-and-after measurements bear out this prediction. However, opponents complain that only one pre-wall measurement was made on the non-wall side of the motorway, so it is impossible for the acousticians to say whether the noise has increased.

Mr Day rejects this, saying the neighbours' real gripe is with the visual intrusiveness of the new wall. They once looked across the motorway from their homes into a bush area. Now there's a shiny metal barrier.

"They are now visually aware of this barrier so they are now aurally aware of the motorway and the noise whereas they weren't before ... if you bowled the thing overnight without telling them they would not be able to tell the difference."

His rejection of the proposition that the wall is bouncing noise into neighbouring homes naturally leads one to question the whole justification for the expensive remedial plans the ARC is contemplating. These involve attaching noise absorbent materials, at a cost of up to $160,000, to the existing wall.

But if there isn't, in fact, a problem, what will this expenditure achieve? Nothing, says Mr Day. "I don't believe they'll notice any difference and that's going to be an unfortunate outcome."

Indeed it is. Not only will it represent a great waste of public money, but it will leave the objectors no happier. They'll likely turn round and vent their spleen on the new product as being no good.

Because no comprehensive noise-level measurements were made before construction, the only sure way to prove who is right is to take the wall down and do a before-and-after comparison. But deconstructing the wall for this experiment will cost tens of thousands of dollars.

And then what? Perhaps it could be chopped up into souvenir-sized pieces and sold off like that other infamous wall in Berlin.