March 29, 2001

The sound barrier between the Auckland Regional Botanic Gardens and the southern motorway is reducing noise at the gardens with no perceptible effect on noise levels at nearby residential properties.

That’s the conclusion of a report by acoustic consultants Marshall Day who have monitored noise levels at the same spot at the same time of day in front of the houses, both before and since construction of the 3.5 metre wall in February.

A delegation of Manurewa residents presented their concerns about the barrier to the Auckland Regional Council Parks and Recreation Committee today

Committee chairman Bill Burrill says while the council will do what it can to soften the visual impact of the barrier as quickly as possible the Marshall Day report should go a long way towards allaying the concerns of residents from the opposite (western) side of the motorway who have complained of dramatically increased noise levels since the wall was erected.

“According to the report, the average of all noise levels taken before construction of the barrier was 72 decibels, compared to an average of 73 decibels after construction,” Cr Burrill says.

“The peak noise level prior to construction was 93 decibels. That has fallen to 92 decibels since the barrier went up.

“Given that it takes three decibels to create a change perceptible to the human ear, the report concludes that ‘there does not appear to have been a noticeable increase in the noise at these properties due to the noise barrier.’”

Cr Burrill says the report also points to a significant noise level reduction within the Botanic Gardens which suggests that the sound barrier is doing exactly what it was designed to do.

“While the ARC is sympathetic towards the plight of the residents, it must be pointed out that according to the evidence we have, the very high noise levels they are enduring are not due to the construction of the Botanic Gardens sound barrier.”

Cr Burrill says both the ARC and Manukau City will continue to monitor the situation.

He says the ARC is also mindful of the visual impact of the barrier and will be planting 100 Tecomanthe plants (the vine which already adorns the entrance to the gardens) to grow over the barrier and soften its appearance.

“Botanic Gardens staff will be urged to make this a top priority and do everything possible to speed up the process.”

The ARC gained a resource consent from Manukau City to build the barrier after reduction of noise levels was recommended as the Botanic Gardens’ priority by a working party considering the gardens’ future direction and planning in 1997.

While Manukau City chose not to publicly notify the consent, the ARC consulted with all residents on the western side of the motorway likely to be affected by the barrier in November/December 1999.

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