Thousands of Otago residents exposed to flooding, liquefaction, new report finds

RNZ News

5 days ago

Lateral spreading happens when liquefaction stretches and tears the ground. This example happened during the 2011 Christchurch earthquake.
Photo:
Sarah Bastin
A new report has found thousands of people and buildings, including homes, are potentially exposed to flooding and liquefaction in Otago.
The Otago Regional Council report used existing data to map the natural hazard exposure risks for people, buildings and critical services. It is the first comprehensive assessment for the entire region.
The report found the greatest exposure was from river and lake flooding and liquefaction hazards.
"Totals of greater than 30,000 people and buildings, including >10,000 dwellings, within the Otago region are located in areas identified as potentially subject to each of these hazards," the report said.
Most of that exposure was located in and near Dunedin, with 39 of the 117 community areas being classed as having a 'high exposure' - which meant an area that had a high number of people or buildings within a mapped hazard area, not that an event was imminent.
This included the floodplains that were in the council's and Lower Taieri flood protection schemes, but people and buildings within those areas were considered to be 'potentially exposed'.
The report assessed 90 critical community facilities across the region - important buildings in a post-disaster response including hospitals, fire and police stations, or emergency operation centres.
Of those, 23 were at risk of flooding and 35 were exposed to liquefaction across the region.
Queenstown, Wānaka and Dunedin all had relatively high exposures to hazards involving slope stability including landslides and alluvial fans.
There were about 500 people and 1100 buildings exposed to coastal hazards including tsunamis and storm surges, mostly around Dunedin and Clutha.
The council's natural hazards manager, Dr Jean-Luc Payan, said the data would help to inform future planning to reduce risk. It would also show where they should prioritise future resilience and hazard investigations, as well as aid emergency management.
"This work is not about predicting when an event might happen," he said.
"It's about identifying where exposure exists so we can make smarter decisions about resilience, planning and investment."
The council's senior natural hazards analyst, Tim van Woerden, said it was a living dataset that would continue to be refined as more detailed information was sourced.
"These terms may sound technical or worrying, but it's important to remember this analysis is about where we focus effort to reduce exposure - not about predicting events or sounding alarms," he said.
The council's natural hazards prioritisation programme is due to begin in the upcoming financial year.