More than 3700 New Zealand rivers may be at risk of earthquake-related flooding, according to research supported by the Natural Hazards Commission Toka Tu Ake.  

The findings stem from University of Canterbury PhD student Erin McEwan’s work to create a world-first database tracking how quakes have influenced rivers.  

Her studies show how ground fractures can cause rivers to shift, flood or be blocked – creating dams or lakes that flood years after an initial quake.  

“This is a hazard that hasn’t had much attention before,” Ms McEwan said. “But in New Zealand, where we have thousands of rivers and lots of active fault lines, it’s inevitable that they will intersect and interact.”

She says the 1987 Edgecumbe earthquake caused land to slump into the floodplain of the Rangitaiki River.

The area has since been exposed to flooding, including a 2017 event that forced 3000 residents to evacuate.

“It’s a very real hazard that we see again and again after large earthquakes,” Ms McEwan said. “This research gives us tools to start predicting where those risks might be highest.”

Ms McEwan and her team analysed 52 historic ground ruptures that affected rivers across the world, and combined the information with New Zealand fault maps and flood models.  

She hopes the database can help communities conduct flood mitigation work that addresses quake risks. 

“We can’t stop earthquakes or floods – but we can help people be ready for them. My goal is to get this into the hands of councils and planners so they can run their own ‘what if’ scenarios and make smart decisions for their communities.”  

NHC research head Natalie Balfour says knowing where flooding is likely after a quake provides “a powerful new tool to protect people and properties.

“Damage from earthquakes isn’t just caused by shaking, which is why research that looks at the suite of related hazards is so important – it helps us understand the full picture of earthquake risk and gives decision-makers the science they need to plan ahead.”