A section of State Highway 1 closed since August will continue to be closed indefinitely, despite Waka Kotahi agreeing to do $14 million of emergency works in the area.

The highway has been closed at Mangamuka Gorge, south of Kaitāia, after 16 slips and heavy rain flooded the area on August 17 and 18.

Usually, the road would see 1300 vehicles a day. They now have to use SH10, a detour adding 30-60 minutes each way – causing some people to quit their jobs.

Waka Kotahi (NZ Transport Agency) does not know how the slips can be fixed, how long it will take and how much it will cost, spokesperson Randhir Karma said.

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Investigation and design work is under way, with a funding application to be submitted to the Waka Kotahi board early in 2023, he said.

“It’s important that we get the decision-making process right and there are many factors to balance including resilience, safety, climate change, affordability, as well as economic and community impacts,” he said.

However, the board has agreed to spend $14m on emergency works to protect SH1 from further damage – such as sealing cracks, drainage work and slip clearing – as well as SH10 slip work and bridge strengthening, Karma said.

Initial work is expected to be finished by March 2023, but SH1 will remain closed at Mangamuka Gorge, except for restricted access for locals and emergency services.

The money is on top of $16.2m spent on slip repairs in the gorge, after a one-in-500-year storm in July 2020 closed the highway for a year.

Far North District Councillor Ann Court said estimates she’d been told were around $50m to $100m to reopen the road, or $200m to $500m to make it more resilient to heavy rain.

She stressed these were estimates only.

Court said it “got her hackles up” when the Waka Kotahi board also asked staff to provide more information on abandoning Mangamuka Gorge.

Slips have already forced the transport agency to abandon one highway – SH3 at Manawatū Gorge – replacing it with a new $620m highway between Ashhurst and Woodville.

Court said it concerned her the board were looking into what they called a “managed retreat” of the route.

However, similar investigations were done after slips closed State Highway 6 in Marlborough and earthquake damage closed SH1 in Kaikoura, but both were rebuilt.

“I understand why they are doing due diligence … They’re saying ‘we cannot continue to pour money into roads that will continue to fail’.”

Such hard conversations were likely to continue across the country due to climate change creating more heavy rain, Court admitted.

But she said it was important the Far North is not forgotten just because it is at the top of the country.

“I want assurance that we’re getting the same level of service as the rest of the country.”

Costs compared

If SH1 at Mangamuka Gorge costs up to $500m to be built better, here’s how that cost would compare to some of the biggest roading projects in the country: