Christchurch tsunami evacuation routes tested in state-of-the-art computer modelling

Friday, 7 June 2019

An animation of the tsunami caused by the 1868 magnitude 8.5-9 earthquake offshore from the Chile-Peru border region. It is the only tsunami known to have killed anyone in New Zealand since the arrival of Europeans.

Coastal Christchurch residents confident they can escape a tsunami threat in 10 minutes may have to think again.

State-of-the-art computer modelling – used to predict the movements of refugees escaping war zones – is helping design a tsunami evacuation plan for the seaside suburb of Sumner.

The software simulates how the 5000 residents would respond if a huge wave triggered by an offshore earthquake overwhelmed the area.

The agent-based model was used to see how quickly Sumner's 5000 residents could reach safety if a tsunami struck.

During the test, 'agents' try reach safety after evacuating their homes, work or the beach. Their success directly relates to the level of preparedness they have been programmed with.

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The red pips are the residents, who are moving to higher ground out of the evacuation zone. They are moving across open spaces and using the roads like people likely would.

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Danielle Barnhill, left, and Laura Tilley, masters students in disaster, risk and resilience have co-organised the tsunami workshops in Sumner.

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Research co-producer Thomas Wilson, associate professor in disaster risk and resilience at the University of Canterbury, said a large enough wave could inundate much of low-lying Sumner.

Without a clear evacuation plan, the modelling shows people tend to take a 'selfish approach' in getting to the hills.

'That's a very rational response but if everyone goes the same route at the same time then they become congested and people can't get out.

An earthquake from the Hikurangi subduction zone could generate a devastating tsunami for the east coast of New Zealand.

'You might think, 'I can get up that hill in 10 minutes', but you won't if you've got people blocking the way and someone has left their car in the middle of it all.'

The research will be unveiled during two workshops next week. Organisers are keen for residents to attend so they can gather local knowledge to combine with the digital data.

'The model can only tell us so much. We want people to tell us how they would react,' Wilson said.

'By having the community input it gives people the chance to directly influence the recommended routes.'

A 'distant-source tsunami', caused by a magnitude-nine earthquake on the subduction zone off the coast of Peru and Chile, was 'probably the greatest risk to Christchurch', he said. It could take 12 to 14 hours to reach New Zealand.

The second possible tsunami trigger would originate from the Hikurangi subduction zone, which runs about 50-100km offshore from Gisborne to Marlborough.

'If a large tsunami struck, much of the Sumner suburb would be inundated by about a metre, but possibly multiple metres. But it's the velocity of the wave and the debris that would cause the damage,' Wilson said.

Laura Tilley, a postgraduate science student at University of Canterbury, said Sumner's topography made the area vulnerable to a tsunami.

'There is one road out, so you are very restricted in terms of ways to evacuate. We really encourage people to evacuate by foot or bike in the case of a tsunami, and to head up the valley to higher ground as opposed to inland.'

The Sumner model was produced by a team from the Christchurch City Council, Civil Defence Emergency Management, Environment Canterbury, GNS Science, Massey University and University of Canterbury.

GNS tsunami scientist William Power said in smaller communities it was possible to stage evacuation drills to see how people would react, but that was not possible in larger areas.

'Sometimes the maps miss things and that is what you get from the workshops. We are interested in refining the model with help from the people who live there,' he said.

The workshops are on June 11, with sessions at 1pm-3pm and 7pm-9pm, in the Sumner Centre, Puoro-Nuku Hall on Wakefield Ave.

- Additional reporting by Jake Kenny