Contractors clearing a slip from State Highway 6 near Murchison. Photo: Supplied / Waka Kotahi
The New Zealand Transport Agency is considering options for realigning part of State Highway 6 in Westland to increase the road network's resilience in future weather events, but such a fix would take years and is likely to cost hundreds of millions.
The highway between Haast and Knight's Point on the West Coast closed during heavy rain on Saturday and is not expected to re-open for at least a week.
Rockfall is still occurring at the site and further heavy rain is forecast.
A state of emergency was declared in South Westland on Saturday, with Franz Josef experiencing its wettest 24 hours in more than four decades.
NZTA central South Island system manager Mark Pinner said the volume of rain had been unprecedented, and the worst-affected part of the highway was the 10km stretch between Haast and Ship Creek, known locally as the Epitaph Slip.
NZTA had been monitoring the site in South Westland since a slip occurred in 2012, using instruments to measure groundwater and ground movement. In 2016, it announced a $1.5 million work programme for the site, following a recent geotechnical review.
It said at the time that erosion was occurring on the slip face itself and below the road, with a larger geological process generating deep-seated movement adjacent to and north of the slip.
Locals have expressed frustration that there had not been more investment in the site, a vital link for the many tourism businesses on the coast.
Pinner said there was no simple solution for the site - which was among the most difficult to manage on the country's road network given the rockfall risk above the road, slip risk below, and complex underlying geology.
He said NZTA was working to increase resilience along the highway and potentially develop alternative access. There was a lot of work still to be done to determine if there was a safe, resilient alignment inland, which was likely to cost "hundreds of millions of dollars".
"Just three weeks ago we signed off on a business case to actually look at an option as to how we can indeed make the road secure from Knight's Point all the way through to Ship Creek, what those options are, what it would cost, what the timeline is so we can give the community some confidence."
Photo: Supplied / NZTA
Meanwhile, contractors had spent the last three days assessing the stability of the site at ground level, but there was still some movement, with rock falling onto the road from a new area on Monday.
"That just means there is a new face we have to look at, maybe a bit more rock that we do need to stabilise to make sure it does not fall on vehicles when we reopen the road."
The movement that had led to cracks in the road surface at the southern end had stabilised, with crews now working to ensure there was no more water running through the site.
Up to 80mm of rain was forecast for the end of the week, and Pinner said they would be closely monitoring the site for any further movement.
"We do realise how important it is to the community ... we know that businesses need this road, we know it's a key lifeline. We are speaking to all the key parties such as Department of Conservation, Westland District Council, Development West Coast, Glacier Country and we are doing our best to keep everyone informed."
He said the road would be progressively reopened - first to a single lane during daylight hours, before a full reopening.
An update on the road status was expected at 5pm on Sunday.
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