Jamie Morton

Jamie Morton is science reporter at the NZ Herald.

Locals want raid sirens for tsunamis

Bay of Plenty group trying to convince council war alarms best for disaster duty.

Steve Morris says the air raid sirens are cheaper and more effective than those the council favours. Photo / APN
Steve Morris says the air raid sirens are cheaper and more effective than those the council favours. Photo / APN

A group of Tauranga residents worried about tsunami alarms proposed by their council have sought their own solution - ultra-loud air raid sirens.

But the city's mayor has concerns over the test blasts the Papamoa Progressive Association has organised at different spots along the coastline next Friday morning.

Association members resolved to undertake their own tests after frequent approaches by locals over the issue, spokesman Steve Morris said.

Tauranga has about 51,000 residents in coastal areas who are vulnerable to a large tsunami.

Civil Defence maps show how Mt Maunganui and Papamoa would be devastated if an "extreme" tsunami hit the Western Bay of Plenty, forcing 35,000 people to flee for their lives.

A 6.75m surge would smash through Tauranga's entire low-lying coastal strip, inundating about 19,000 homes and 2000 commercial premises.

The association eventually agreed to take up an offer by Tactical Tooling, the manufacturer of a modern version of the traditional World War II air raid siren, which had put in an unsuccessful bid to Tauranga City Council.

He felt the sirens were a cheaper and more effective option than the 60 small electronic sirens proposed by the council.

"These sirens only need to be turned over once a year, and there are examples around the country of sirens that are 60 years old and still in service," he said.

"When you're dealing with a low-probability event, any warning measures need to be cost effective. Our view is, why spend $800,000 when you can have a much cheaper system for $200,000 that could last for 50 years?"

Tauranga Mayor Stuart Crosby said he had no issues with the tests going ahead, but did not want to see them jeopardise the tender process for another system still in the design and build process.

"We also hope to apply to other agencies for funding and we don't want a battle between what is best to put that funding to jeopardy, otherwise that may fall back on the ratepayers."

Mr Crosby said the tsunami warning sirens had to be distinguishable from other sirens - an issue the electronic alarms addressed.

"The frustration we all have is there is no national standard for this from Civil Defence, so you are at risk of having a series of ad hoc sirens up and down the coast," he said.

"I'm quite comfortable with what Steve Morris and his group are doing, but whether it would add value to decision-making, we'll just have to wait and see."


The sirens

The two generator-powered sirens to be tested can generate 105 decibels of sound at 50m away, and under clear conditions could be heard 30km away.

The sirens, to be hoisted on cherry pickers, generate a maximum decibel-level of 113 at 10m away from them.

The level drops to 31 decibels at 10km away.

Organisers say the tests, lasting three minutes, won't pose any hearing damage risks.

140 decibels shotgun blast

130 decibels jet taking off

115 decibels power saws, chainsaws

113 decibels maximum sound pressure level of sirens (from 10m away)

100 decibels grinding metal, noisy lawn mowers, MP3 player at full volume

70 decibels noisy office

31 decibels level of sirens from 10km away

- NZ Herald

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