One of the land slips that has forced evacuations and red or yellow stickered homes at Muriwai. Photo: RNZ / Nick Monro
Auckland Council's head of engineering resilience says it could be six months' wait for homeowners on two roads affected by landslips at Muriwai, before they know if they can live in their properties again.
Geotechnical engineer Ross Roberts told Checkpoint it would be one or two months before the future of the affected properties could be confirmed, as the earth around them was still unstable.
However, some would face a much longer wait.
"It's going to vary depending on particularly how far they are from the slope... The ones further away from the slope, we're likely to be able to get a good idea, within a month or two... it really does depend on how those slopes respond to changes," he said.
"It could certainly be longer... Examples from other areas around New Zealand have shown that where you get landslides, it can take six months or sometimes longer before you can actually have enough information to give people confidence to be able to get back into the homes in the worst locations."
There are 128 red-stickered properties in the West Auckland beach settlement, with an additional 48 yellow-stickered.
Roberts said detailed surveys were being carried out using a helicopter equipped with Lidar (Light Detection and Ranging), a remote sensing technology that uses light in the form of a pulsed laser to measure ranges to the Earth.
Surveys are being carried out once a week during weekends and are being compared from week to week.
"It can tell us how it's moving," Roberts said.
"I wouldn't want to give people false optimism at this stage" - Geotechnical engineer Ross Roberts
"We just today got back some results that show us that from the first survey to the second survey one week later, in areas there was between 1 and 2m of movement in that ground.
"So there's still a fair amount of movement happening in some areas, particularly around the tops of the landslides that occurred a few weeks back."
He said further rainy weather recently would have triggered some further movement on top of what was typically expected after slips.
"I wouldn't want to give people false optimism at this stage," he said.
"As time goes on we will get more information and more and more people will be able to get back into their homes, but there'll be some who are in particularly challenging locations where we just won't be able to give that confidence for quite some period of time."
Staff were working hard to downgrade red-stickered properties on Domain Road, which was particularly hit by the cyclone, he added.
"We know that we can't get every single property changed overnight. But what we can do is get more detailed assessments, get more detailed modelling done, which will allow us to identify the ones that are lower risk from the ones that are higher risk, and enable access to as many of those as we can."