No timeline for reopening SH1 at Mangamuka Gorge after slips worse than thought

Thursday, 29 September 2022

Drone footage of slips at the Mangamuka Gorge on State Highway 1 taken soon after heavy rains in the Far North caused significant damage in August 2022. (This video has no sound)

A section of State Highway 1 in the Far North, which has been closed off since August after heavy rain, is far more damaged than initial assessments showed.

There is no timeline of when it will reopen.

Heavy rain on August 18 and 19 damaged parts of State Highway 1 and 10 in Northland, forcing closure.

SH1 has been closed at Mangamuka Gorge, just south of Kaitāia, since heavy rain on August 18 and 19 caused a series of slips.

Waka Kotahi NZ Transport Agency regional manager system design Randhir Karma said geotechnical investigations were complete at 16 slip sites and though information was currently being analysed, the Mangamuka Gorge was facing a long-term resilience issue.

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Northland residents are being warned the severely damaged Mangamuka Gorge could take ages to repair after it was taken out in a storm.

He said the recent slips were much worse than damage caused by bad weather in June 2020.

“As a result of the 2020 weather event, two slips were significant enough to keep the road closed for almost a year,” Karma said.

“There are now at least five slips of similar or greater size and severity, despite the underlying repair work we did after the 2020 event holding up well.”

The heavy rain left 19 slips on SH1 at Mangamuka Gorge, cutting a trail of destruction through the highway.

Geotechnical assessments across secondary sites would continue, to help Waka Kotahi paint a clearer picture of the full extent of the damage and ground conditions within the gorge.

The agency couldn’t estimate the cost or the timeline of the work needed to reopen the SH1 corridor for the area, he said.

For now, Waka Kotahi would partner with mana whenua, stakeholders and key experts to review the roles of SH1, SH10 and local roads in order to provide a resilient transport network for the region.

Karma said this would help establish the work needed for the highways, including examining options, assessing costs, scoping risks, procurement, and implementation.

“The feedback received from our partners will feed into an options' assessment which will recommend a preferred way forward.”

Karma said while work would be accelerated for the project, they would also be thorough to achieve a state highway north that can withstand severe weather, for example.

“Though we don’t yet have all the answers, by working together with key Far North community members and experts, we are confident that together we will deliver a solution that will strengthen and benefit the region for generations to come.”