Days Track closed after 2011 floods and did not reopen until 2017. It was closed again after slips during the August 2022 flooding. Photo: RNZ/ Samantha Gee
New research shows the area affected by the active landslide known as the Tāhunanui slump is not as large as initially thought.
But a year on, about 25 families in Nelson have not been able to return to their homes, which remain red and yellow stickered due to ongoing land instability and the risk of slips.
Toka Tū Ake EQC chief readiness and recovery officer Kate Tod said it commissioned a geotechnical report from Tonkin & Taylor after the floods in order to get a better understanding of the most recent land movement.
Additional boreholes and equipment were installed across the slump to monitor and measure both the ground movement and the groundwater levels.
While quite technical, Tod said the report gave a better understanding of the depth, the extent and the mechanisms controlling the instability on the Tāhunanui Hills.
"The good news is that the area impacted by the deep landslide is not as large as we thought, and that the other positive is that we know that the groundwater levels have returned to what they were [prior to August 2022]."
Movement of the slump has been documented since the late 1800s and Tod said due to the ongoing instability, there remained a risk of further damage to properties during heavy rain.
After the atmospheric river that caused widespread damage across Nelson last August, there were 39 EQC claims for properties on the Tāhunanui slump, and Tod said the majority of those had been settled.
A red stickered home in Nelson. Photo: RNZ/ Samantha Gee
Under the EQC Act, compensation for damaged residential land amounts to the lesser of either the cost to repair or reinstate the damaged land, or the land value.
Tod said there were situations around the country, where people could not move back into their homes, because of the potential risk of land coming from another property, which was really challenging.
RNZ has spoken to homeowners who cannot return to their homes due to the inundation risk, but are not entitled to an insurance or EQC payout because their homes are not damaged.
The report has proposed potential remediation options for different areas that include: improving the control of stormwater flows, subsoil drainage, planting vegetation, installing deflection barriers and catch fences and anchored shotcrete slope protection.
"We are likely to have more of these events, so the more knowledge and data we have at our fingertips, the better and so that we can think about how can we, build back better and more resilient properties.
"It's something that as a country, we're going to have to face more and more questions about where we're building, and where there are repeated events, can we actually put people back in those areas?"
Grenville Terrace in Nelson where many houses remained red or yellow stickered. Photo: RNZ/ Samantha Gee
Nelson mayor Nick Smith said landslides and the ongoing management of the Tāhunanui slump would be challenging issues for the Nelson City Council for decades ahead.
He said the main priority in the ongoing flood recovery was to address the 25 properties where the owners had still not been able to return home.
He said the immediate issue off the back of the EQC report was to resolve the outstanding land claims for properties on the Tāhunanui slump.
"There are infrastructure improvements that we can make in that area that we want to get on and prioritise, then there is the long-term issue as to how this council and community best manage that largest urban landslide in New Zealand."
Smith has called on the government to extend the same support it has to those whose homes were damaged in Cyclone Gabrielle, specifically seeking potential buyout options for homeowners where remediation was not economic.