Repaired SH1 over Mangamukas in Far North passes first heavy rain tests

Some of the team who worked on rebuilding SH1 over the Mangamuka Gorge in the Far North over two years. Their work has passed its first major test.

The two-year $204 million rebuild of State Highway One over Mangamuka Gorge in the Far North has passed its first major test - heavy rain and strong winds.

It was storms and heavy rain that closed the road for so long, so last week’s heavy rain - the first since the gorge reopened on December 19 - had people anxious.

But despite up to 73mm of rain, everything held up well, NZ Transport Agency Waka Kotahi (NZTA) said.

And while heavy rain at the weekend brought down a small slip on the southern side, it was quickly cleared up. That slip was not inside the repaired area.

NZTA opened the troublesome stretch of State Highway 1 through the Mangamukas after more than two years and $204 million of work, following a closure caused by more than 30 major slips.

A 1-in-500-year storm caused major slips and forced its closure in July 2020. The gorge opened in June 2021 and repairs cost $16.2m. The road was destroyed by slips during another major storm in August 2022, and yet another storm in 2023 delayed repairs and bumped up costs from $160m to $204m.

NZTA project director Mark Ware said the road held up well last week, despite the heavy rain.

SH1 over Mangamuka Gorge, in the Far North was closed for almost two years after storms devastated the hills. The new road survived the first storm since reopening with flying colours.

‘‘This is testament to the repair work done over the past two years and the hard work put in by everyone involved,’’ Ware said.

‘‘State Highway 1 through Mangamuka Gorge reopened to all traffic, including freight, just before Christmas and it’s been great to hear many people have been enjoying travelling the new road over the holidays.’’

He said the road was rebuilt over 22 months, with more than 1,300 piles and 300 anchors installed, the road resurfaced, guardrails upgraded, and drainage improved.

‘‘This work has made the road a safer and more resilient route, reconnecting our Northland communities.’’

Ware said there is still some ongoing work required and crews are to complete final works on the remaining slip sites. They are completing the installation of the remaining ground anchors on the last two slip sites, and undertaking minor tasks such as filling in anchor pockets and installing swale drains.

‘‘The road will stay open throughout this work, with temporary traffic management in place near the worksites. This may include lane closures, reduced speed limits, and temporary traffic lights or stop/go. Work is expected to be complete by the end of April 2025,’’ Ware said.

‘‘People travelling through the Mangamuka Gorge can help keep everyone safe by driving with care, adhering to the posted speed limits and following the directions of traffic management staff and signs.’’

At the peak of the Mangamuka work approximately 75 per cent of the workforce, and many of the suppliers, were from the Far North community.

”Being able to reopen the road is the culmination of their hard work and dedication – the end of a challenging but rewarding journey.”

Since the road reopened, Far North businesses have welcomed a financial boom from the extra visitors.