The models present a scenario of what might happen in a tsunami evacuation in Napier.
A full 60 minutes after a long-strong earthquake in Napier triggers the risk of a tsunami, people could still be crossing a harbour-facing bridge trying to get to high ground.
That’s the reality presented to the city, and particularly residents who live in Westshore, in a New Zealand-first tsunami evacuation model covering the entire city.
The GNS-created model turns people into red dots and simulates a working-day scenario of what might happen when shaking begins in the Hawke’s Bay city, which previously experienced the tragedy of a devastating earthquake in 1931.
Scientists have since discovered an even bigger threat to Napier and most of the east coast of the North Island, from the off-shore Hikurangi subduction zone. Scientists have projected one-in-four odds of a magnitude-8.0 event occurring on its southern reaches within the next 50 years.
Most would occur in a tsunami that would follow a 9.1 earthquake - with that toll still assuming 70% of people were able to evacuate.
The simulation now created by GNS is a simplification.
Seven minutes after a long-strong earthquake, Napier's inner city roads will be heavily congested with people trying to get to high ground. Photo / GNS simulation
A spokeswoman said in reality what occurred after an earthquake would be a “very complicated” situation.
Roads could be cracked, uplifted, or swamped by liquefaction, buildings or trees could be downed by landslides, bridges might not even be passable on foot.
“The evacuation results will vary depending on the time of day,” a GNS spokeswoman said.
“Importantly, the modelling of congestion is approximate. The models are based on people evacuating promptly after an earthquake and taking the shortest route by foot.
“In reality, there are many factors that will influence the results such as walking speed, visitor numbers, debris, aftershocks.”
GNS says the animation will support emergency response agencies with their planning and preparedness for a tsunami event.
“[It is] not intended to provide advice on what individual people should do. It is up to emergency management agencies to determine what advice to provide people on how best to keep safe during a tsunami threat.”
The dots themselves tell a story.
For the first couple of minutes, very few people move, still dealing with the shaking and the shock of the disaster.
By five minutes people are pouring out of Napier’s CBD and up onto the hill. By 10 minutes almost every hill-facing street or exit point in the CBD is completely clogged with people movement.
After 30 minutes most of the CBD is cleared out as people make it to the safety of the hill.
But many of those in either Westshore and Awatoto are continuing to move, with a thick red line on the Pandora Bridge suggesting a significant congestion point.
About 45 minutes after the quake, evacuees continue to file across the congested Pandora Bridge from Westshore to Napier Hill. Photo / GNS simulation
Few, if any, decide to take the Hawke’s Bay Expressway bridge instead of Pandora and some of the last dots to make their way towards the hill are from Hawke’s Bay Airport.
The simulation video stops at 60 minutes after the quake, with a thick red line of people now mostly over the Westshore Bridge, but still on their way to the hill.
A public presentation tomorrow at 6pm at Napier Boys’ High School Hall will show the simulation, among other educative features.
GNS says the presentation will use the updated evacuation maps and highlight the importance of travelling on foot or by bike during a tsunami evacuation and the need for multiple evacuation routes.
The Viewing Platform on Marine Parade beach, Napier, which is the first city in NZ to have a full evacuation model developed. Photo / Getty
This research is part of a three-year project called “Agent models of tsunami evacuation behaviour to improve planning and preparedness”, funded by the Ministry of Business, Innovation and Employment (MBIE) Endeavour Fund.
William Power, a tsunami modeller at GNS Science, said the new models provided valuable insights to support safer evacuations.
“Evacuating on foot or by bike is strongly recommended for those in urban areas to help all people reach safety as quickly as possible.”
The presentation will also include preliminary simulations of evacuations from Westshore and Bay View that include vehicles as well as pedestrians.
Shane Briggs, the acting group manager of Hawke’s Bay Civil Defence Emergency Management Group, said knowing alternative routes was critical because some roads may be blocked or unsafe after an earthquake.
“Practising your tsunami hīkoi helps you act quickly and safely if a real evacuation is needed.”
He said it was crucial to understand the natural warning signs of a tsunami.
