City looks at ultra-loud tsunami warning sirens

Ultra-loud warning sirens of the type used in the United States' "tornado alley" are being mooted for tsunami-prone Tauranga.

The city council is proposing a warning system with sirens like those used in the American Midwest, which are loud enough to wake people 1.8km away from them.

A report to be put to councillors today says the sirens are so powerful they should be placed at least 100m away - and facing away - from homes, on buildings at least 30m tall.

No sirens of their kind have been used in New Zealand, and each costs $130,000.

Tauranga has about 51,000 residents in coastal areas who are vulnerable to a large tsunami. A survey by the Bay of Plenty Times of 250 city residents found 80 per cent were unprepared.

Civil Defence has released maps showing 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.

A recent council report said a tsunami with a one-metre wave height was predicted to hit Tauranga every 80 years, a 2.5m wave every 322 years and a 5m wave every 3300 years.

The Bay of Plenty's civil defence emergency management group had ranked air-raid-style sirens 21st out of 29 systems that could be used to warn residents of impending disaster. But Japan's tsunami prompted the Tauranga City Council to make its own investigation.

"The original report we received did not include sirens as a warning option and, clearly, this one puts a whole new perspective on it," Tauranga Mayor Stuart Crosby said.

"We will also need to engage with Western Bay of Plenty District Council so there is a uniformity in warning systems.

"There's no one national warning system, particularly for our coastline, and that seems a bit ridiculous.

"The practical reality is that we may never need them, but also we may need them tomorrow - such is the nature of nature."

Other options for noise warnings include portable sirens able to be mounted on vehicles or carried by helicopters, power-pole-mounted sirens and sirens mounted on 10m poles that could wake residents within a 600m radius.

IN OTHER REGIONS

* Northland: 70 tsunami sirens to be commissioned between Mangawhai and Bland Bay.

* Auckland: Tsunami sirens are installed in Rodney and Waitakere, and a telecommunications system has been developed for Rodney and the North Shore. Sirens for Orewa have been allowed for in Auckland Council's draft capital expenditure budget.

* Hawkes Bay: Napier has sirens, and Hastings District Council and Wairoa District Council are considering the systems.

* Gisborne: Proposed options include sirens, signs and a texting system.

* Coromandel: Evacuation plans are being developed for the eastern Coromandel Peninsula. Whitianga discussed preparedness at the weekend.