In a few weeks’ time, West Coasters will be able to find out if their home – or one they’re planning to buy – may be at risk of damage or even demolition in a landslide.
Regional council staff are working on the final parts of a natural hazards portal on the council website that lets the public zoom around on the map and check out the threats posed by nature in a given area.
That included flooding, storm surge, liquefaction and, now, the risk of landslide – triggered either by rainfall or earthquake.
The addition of landslide hazard maps to the portal follows a Regional Landslide Debris Inundation Hazard and Risk Assessment study, carried out by GNS (now Earth Sciences NZ) scientists over nearly three years.
The $207,000 study was commissioned by the West Coast Regional Council Civil Defence team in 2022 to help with its disaster planning.
But it also gives local authorities a new tool to gauge which areas might be unsuited for development in a changing climate.
The council’s senior natural hazards Analyst, Dr Sharon Hornblow gave councillors a condensed version of the lengthy study at their meeting on Tuesday.
Landslides had killed 700 people since the 1840s, making them New Zealand's deadliest natural hazard, she told councillors.
Scientists could not predict exactly when a landslide would happen, but they now had a model that estimated how much debris would come down, and how far it would reach, Hornblow said.
The West Coast study been held up when GNS scientists were diverted by Cyclone Gabrielle and other landslide emergencies, but that had in the end proved useful.
"The science that went into understanding, mapping and modelling landslide risk from Gabrielle and the Auckland events benefitted WCRC’s model… the result is now a leading example of regional risk modelling for landslides in New Zealand,” Hornblow told Local Democracy Reporting.
It was important to note that the maps did not equate to a geo-technical assessment of landslide risk at a specific property but served as a screening tool for areas that might be at higher risk at a given site or slope, she said.
Regional Council chair Colin Smith asked whether staff had considered "socialising" the landslide risk study with West Coast lawyers who did conveyancing work.
“Being a former lawyer, it seems to me that this is a pretty important report that lawyers should be well aware of, in terms of advising their clients.”
He had once advised a client buying a property that the LIM report recorded a landslide in the area 50 years before.
“I advised him of the risk and within 10 years of owning the place,another landslide hit the back of the home …it’s really a live issue for the profession and anyone buying property."
Hornblow said the council was obliged to share the information under new LIM provisions in the Local Government Act.
“When this was commissioned a few years ago, it was for emergency management, but you can’t just hold it as a ‘nice to have’ …you have to make it available, it’s important for legal liability.”
Chief executive Darryl Lew confirmed the regional council had to disclose the study and landslide hazard maps to the three district councils.
“We would be legally liable if we did not … it’s axiomatic it will end up in their LIMs,” Lew said.
The new hazard report would also trigger a plan change to the new Tai o Poutini Plan, once all the appeals were resolved, and it might be that Councils would in future have to take on landslide protection, as well as flood protection, Lew said.
“I have personally overseen the construction of a debris-bund up on Aoraki Mt Cook, so in high hazard situations, where there’s a direct threat to property and life, there is an engineering [solution] but it comes at a cost."
The council resolved to offer a workshop for lawyers and district council staff, to familiarise themselves with the landslide study and its implications.
The Natural Hazards map portal should be live in a week or two, Hornblow said.
By Lois Williams for Local Democracy Reporting
– LDR is local body journalism co-funded by RNZ and NZ On Air.
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