New tsunami maps revealed to help people evacuate holiday hotspot

Christel Yardley/Stuff

Residents of Mount Maunganui and Papamoa have raised concerns about tsunami escape routes

Revised evacuation maps for the Bay of Plenty area have revealed 100,000 people in the holiday and retiree hotspot would need to evacuate quickly with no official warning in the event of a tsunami.

The maps, released on Tuesday by Civil Defence and Emergency Management (CDEM), abandon the traffic light system used elsewhere in the country and instead mark areas at risk of being hit by waves within minutes.

The region’s director of Emergency Management Clinton Naude said: “blue means go.”

“With tsunami, we could be dealing with very short timeframes.”

Tsunami are classed as “high risk” to the region with a “significant threat to people and property” CDEM said.

Bay of Plenty residents recently raised fears to Stuff that they are “sitting ducks” and “condemned to death” in the event of a tsunami, given the lack of high ground and limited escape routes.

Advocacy group, the Eastern Corridor Alliance – formed by residents and businesses – has been pushing for better evacuation routes.

CDEM/Stuff

Civil Defence and Emergency Management (CDEM) has issued updated tsunami maps for the Bay of Plenty, with the message to the thousands of people in the newly-defined 'blue zone' that there may be only 13 minutes or less to get to higher ground.

The Bay of Plenty has two significant subduction zones (active undersea areas) relatively close – the Hikurangi Subduction zone to the east and the Kermadec Trench to the northeast – which could trigger a tsunami, forcing immediate evacuation.

“Major activity in either of these areas could cause tsunami on our coastline,” said a CDEM spokesperson.

Large earthquakes in the Kermadec trench could generate waves of up to 10m high – which could potentially inundate parts of Mauao and Pāpāmoa within four hours, NIWA research has shown.

Scientists from Crown research entity GNS have modelled that an 8.9 magnitude earthquake in the Hikurangi Subduction zone would trigger a tsunami with waves up to 20m on parts of New Zealand’s coast, with as little as 13 minutes to get to safety.

Higher waves would be more likely on the East Coast, but could also hit the Bay of Plenty, and areas of Wellington, said GNS principal scientist Dr Graham Leonard, a natural hazard expert who is part of the national Tsunami Advisory Group and Tsunami Working Group.

There is a one in four – or 26% chance – of such an event in the next 50 years, say scientists.

GNS has now commissioned scientific research over the next two years to further improve tsunami modelling which would result in “a gold standard” for evacuation maps across Aotearoa aimed for mid 2025, said a CDEM spokesperson.

The Hikurangi scenario was the one that gave Graham Leonard “sleepless nights”, as there are currently around six identified areas of New Zealand that lack higher ground for residents to reach quickly in an evacuation.

Areas include parts of Pāpāmoa, Petone in Wellington, Napier, and parts of Christchurch.

GNS Science

The Pacific Plate starts diving under the Australian Plate at the Hikurangi Subduction Zone off the east coast of the North Island.

In a New Zealand first, Pāpāmoa now has a vertical evacuation structure at Gordon Spratt reserve in Pāpāmoa East with capacity for 3800 people to seek refuge at the top, built to withstand tsunami flooding and earthquake shaking and liquefaction.

Consideration of vertical evacuation structures in other parts of the country would be looked into as part of the GNS research, as well as more precise calculation of evacuation times, Leonard said.

Stuff

A computer-generated image from 2011 showing what a 10m tsunami would look like in central Wellington.

About a third of New Zealanders did not evacuate at all or evacuate fast enough.

While there would be fatalities in the event of a large locally generated tsunami such as Hikurangi, they could be vastly reduced with early evacuation, as soon as people felt a long strong earthquake, without waiting for an official warning, he said.

“A third of people not evacuating is concerning. Lessons from Japan showed higher survival rates from those who evacuated early and knew routes.”

Until the new research into tsunami modelling and evacuation times was complete, clearer maps were welcomed, he said.

“Bay of Plenty is at the forefront. Other areas are looking into changing too. Wellington already has blue arrows on roads.”

Tsunami sign boards at beaches and waterways are being updated. There is a new QR code that people can scan.

People were encouraged to practise escape routes, with a mass ‘dry run’ event or tsunami hīkoi on October 19.

You can run if you want, but don’t get in a car.

Bay of Plenty locals were trapped in gridlocked traffic when they tried to reach higher ground after New Zealand’s tsunami warning in March 2021 triggered by a magnitude 8.1 earthquake near the Kermedec Islands.

NZTA modelling shows vehicle traffic would gridlock Bay of Plenty roads within minutes in an evacuation. CDEM advises people to go by foot, bike or scooter.

Christel Yardley/Stuff

Philip Brown, chair of the Pāpāmoa residents association, is concerned areas of Mount Maunganui and Pāpāmoa could be “death traps” in a tsunami.

Pāpāmoa Residents and Ratepayers Association president Philip Brown previously told Stuff that previous maps were “incomplete”, “condemning people to death,” and he ended up in a ditch when he tested his.

New blue maps include an additional zone of higher ground for Pāpāmoa.

“Updated maps use the most recent aerials available, so they capture the current streets and developments. Aerials will be reviewed annually, and we will update them as more development takes place,” said a CDEM spokesperson.

Lessons had also been learnt in the Bay of Plenty 2021 event that people shouldn’t try to reach loved ones first, but focus on getting themselves out, said Leonard.

“Another lesson from Japan – tsunami-tendenko. It’s not callous, but saves more lives. Schools and rest homes have their own evacuation plans. People in Japan who tried to get to others ended up with more fatalities.”

In the Bay of Plenty 2021 event, people trying to pick up school children was a factor in gridlocking, he said.

“Schools drill more than anyone, so be confident that they are likely to evacuate to safety quicker than you could reach them.”

Tsunami evacuation plan

Check maps if you are in an evacuation zone.

Know an escape route and practise it.

If in an evacuation zone, leave immediately after a long strong earthquake – a quake that is either longer than a minute or strong enough that it is hard to stand. Do not delay waiting for official warning.

Head inland or to higher ground on foot or bike. Stay there until official all-clear.

Tsunami hīkoi on October 19.