Manawatū River seen at capacity in Palmerston North during Cyclone Gabrielle. Photo: Warwick Smith / Manawatu Standard / LDR
Palmerston North and Whanganui are the two centres in the Horizons catchment most vulnerable to building damage from flooding, a new study shows.
Various tests were run to simulate what would happen to existing flood prevention methods during extreme weather events.
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The assessment provided first-of-its-kind flood mapping throughout Ruapehu, uncovered the need for greater storm water data collection in Levin, and made sure elected officials weren't underestimating the impact of bigger weather events.
The scenarios were presented to regional councillors on Tuesday, with a round of applause breaking out within the room following the release of this new data.
The report was not to be used by individuals to assess private property for flood vulnerabilities, instead "the risk rankings are there to help to inform strategic planning" for councils, Horizons group manager of catchment operations Dr Jon Roygard said.
"We know people connect to rivers throughout the region for a range of reasons, and population centres and businesses have been built around waterways.
"This connection to rivers does heighten risk from flood events. While we have done some flood modelling before, this assessment fills the gaps where there was no modelling done previously".
"The real value in this is to say, 'where do you want to focus?', he said, "And then we can do more detailed modelling."
Roygard believed this pre-emptive approach should be embraced by councils nationally.
Eighteen months of work went into producing the extensive report on the strengths and weaknesses of more than 50 population centres during different flooding scenarios and weather events.
"Mātauranga Māori is valued and appreciated by Horizons" as this assessment will be utilised across multiple committees and Horizons groups with consideration of how iwi and hapū knowledge can be used alongside the report, Roygard said.
Horizons chairperson Nikki Riley said that the assessment was "enlightening" and something that would be discussed "again and again" for years to come.
Deputy chairperson Fiona Gordon said it is the first flood vulnerability assessment to this level.
"It's really front and centre now... It is complex and it will take us some time to digest, older and newer councillors alike."
More than $4.2 million worth of funding was granted by central government to Horizons through the Cyclone Recovery Flood Resilience Co-investment Fund to do a range of resilience and recovery projects.
Scenarios such as a 1-in-100-year flood were run, with temperature and geographical variables being altered in some tests based on climate change predictions.
Preparing the region for the impacts of climate change through accurate data and sufficient funding was seen as "critical to our purpose", Horizons councillor Alan Taylor said.
Taylor told Local Democracy Reporting, "society's willingness to fund what the future is likely to throw at us is also an unknown, yet highly likely to be an underestimation of what is necessary" to properly protect the region.
LDR is local body journalism co-funded by RNZ and NZ On Air.
