A key Far North road closed by slips might not be fixable due to the huge amount of earth movement, according to one politician.

But even if this year’s slips on State Highway 1 through Mangamuka Gorge can be fixed, Waka Kotahi NZ Transport Agency and local leaders are now scrambling to find a long-term alternative.

The gorge, just south of Kaitāia, has been closed indefinitely since a storm on August 18 and 19, where heavy rain fell on top of a record-wet winter.

But a one-in-500-year storm in July 2020 closed the same stretch of road for a year, with slip repairs costing $16.2 million to fix.

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* State Highway 1 to Kaitaia opens a year after devastating Northland floods

A serious crash on the closed road last week is another example of the road’s dangers.

The problem is not due to a lack of maintenance but Mangamuka Gorge’s steep terrain and “plastic” soil type, which expands when wet and shrinks when dry, said Far North deputy mayor Ann Court.

“It looks like an earthquake – there’s these massive fractures up to 1m high, through the road there’s just so many of them, they go on forever,” she said.

“No matter how much money we throw at Mangamuka, that road will fail again. All the experts are telling us that there’s no way to engineer that road so that it will not be vulnerable to this type of weather event.”

Mangamuka Gorge – also called Maungataniwha, which translates to monster mountain – usually carries about 1300 cars a day.

Waka Kotahi regional manager system design Randhir Karma said geotechnical investigations at 16 slip sites were now being analysed but further geotechnical assessments were needed to get a clear picture of the damage.

The agency is unable to estimate the cost or time to reopen the road, but acknowledges Mangamuka Gorge is “facing a long-term resilience issue”, he said.

Everything from tunnelling under the mountain to permanently closing the road was put on the table at a Waka Kotahi workshop with about 30 community representatives last week, Court said.

There were about a dozen alternatives, including upgrading SH10 to become SH1, upgrading an alternative western route through Broadwood, and creating a new route from east to west, such as through Otangaroa or Takahue Saddle, she said.

Each of these options has its challenges and will have people who do not want their road turned into a state highway, Court acknowledged.

Even SH10 often floods at Kāeo and runs through townships like Coopers Beach and Taipā, she said.

More details about each option will be presented to Waka Kotahi’s board in November, Court said.

But Kaitāia Business Association chair Andrea Panther said people at the meeting told Waka Kotahi the Mangamuka Gorge needed to be fixed.

The gorge is the closest route between Kaitāia and the rest of the country, with other alternatives adding 30 to 40 minutes to a trip which some people do daily, she said.

“I guess, until we see the geotech and engineers’ reports, we can’t be sure that Waka Kotahi will do the fix option that we want.”

The road closure is causing anxiety in Kaitāia for both residents and businesses, and has added a cloud to plans for summer, when the area usually swells with visitors.

“We’re all dreading what’s going to happen in summer if no one will want to come north because of the congestion [on SH10]. We have some of the best beaches around and this summer should be a boom time to make up for Covid.”

Meanwhile, police are investigating a crash on the closed section of SH1, and people are questioning what the driver was doing in the sealed-off area.

A woman crashed her car on September 29 but spent a night waiting to be discovered due to the lack of traffic on the road.

A police spokesperson said the sole occupant of the vehicle was transported to hospital with serious injuries and is continuing to recover from those injuries.

Kaitāia deputy fire chief Ross Beddows said the car was precariously wedged on a tree and the fire brigade had to secure the vehicle while ambulance stretchered the woman out.

But the car was not badly damaged and the woman may have been injured after she got out of the car, he said.

“We were a bit bemused as to how she was in the gorge – she was very lucky that the two contractors found her when they did.”

A Waka Kotahi spokesperson said it has 24/7 traffic management at Mangamuka Gorge, but access is still required for residents who live within the gorge, contractors and emergency services.

“Sections of slips have been levelled out where possible to ensure the road is usable for these vehicles at crawl speed.”

The agency would not comment further while the police investigation was underway.