New Modelling to Shed Light on Tsunami Risks

Published: 04-Dec-2019

The Waimakariri District Council is welcoming new modelling that could help the District better prepare for the risk of tsunamis.

Environment Canterbury (ECan) recently commissioned GNS Science to model the impacts of various tsunami scenarios for specific parts of Canterbury. The results show that in worse-case scenarios, flooding could travel further inland than previously thought.

While modelling was focussed on Christchurch, it included the Waimakariri River mouth and has implications for coastal areas in Waimakariri including Kaiapoi.
As a result, ECan is commissioning multi-scenario modelling for the entire Pegasus Bay, which will help local authorities such as Waimakariri District Council update their tsunami preparations and evacuation zones. The results are expected to be available later next year.

“It’s important that we have a full picture of how it could affect our District before making any changes. The upcoming modelling for Pegasus Bay will allow us to make decisions based on the best science available,” says Waimakariri District Emergency Management Advisor, Brennan Wiremu.

It’s thought that the largest tsunami risk to the Waimakariri coastline, in terms of the areas that could be flooded, would be generated by a very large earthquake off the coast of South America, which would take approximately 12 to 15 hours to reach Canterbury. Such large events are rare, with estimated return periods of at least 500 years – possible in someone’s lifetime but unlikely.

Smaller tsunamis that could flood low-lying coastal land, or create strong currents in the sea and river mouths, are more likely but still uncommon. They include tsunamis from across the Pacific Ocean as well as those created close to our shores.

Brennan says that Civil Defence is ready to respond to the threat of a tsunami but encourages residents to also have their own preparations in place at home.
“Our message hasn’t changed, if you feel an earthquake that is long or strong, get gone. Don’t wait for an official warning,” he says. “In all other cases, check the Council’s website or Facebook page for up-to-date information.”

He also urges people who work or spend time in Christchurch to familiarise themselves with the new tsunami evacuation zones produced for the city. More information can be found on the Christchurch City Council website.

The Council will update residents once the modelling for Pegasus Bay is completed and the tsunami evacuation zones are reviewed late next year. A list of frequently asked questions can be found on this page.

More information about the recent report can be found on ECan’s website.

Tsunami Safety Tips:

  • Long or strong, get gone – if you feel a rolling-motion earthquake for longer than a minute or a strong earthquake that makes it hard to stand up, you need to leave. When the shaking stops, head immediately to the nearest high ground or as far inland as you can.
  • Stay Informed – keep checking official Civil Defence channels for up-to-date information. These include the Waimakariri District Council website and Facebook page, and radio stations such Compass 104.9 FM and Radio NZ.
  • Be prepared – emergencies can happen anytime, anywhere. Check out for tips to make sure you’re prepared.
  • Have a plan – have an evacuation plan and possible route for your household, including pets. Think about where you would go and, if possible, make a plan with family or friends who live outside the tsunami zone to stay with them if you need to evacuate. Share any official warnings you hear with family and friends near the coast.