SH1 over Mangamukas in Far North again closed by slip after $204m repair job

The latest slip that has closed SH1 over Mangamuka Gorge, in the Far North, pictured on Wednesday morning.

Three storms in two weeks have proved too much for SH1 over Mangamuka Gorge, with the road again closed due to a slip on Tuesday.

It’s the second landslide in a few days to close the gorge highway.

NZ Transport Agency Waka Kotahi said contractors had been monitoring movement on the hillside following recent heavy rain, and the slip was expected. Contractors are on site working on the damage.

This slip on SH1, Mangamuka, on Tuesday evening has again closed the road.

The highway was still closed on Wednesday evening, with NZTA Waka Kotahi contractors working to clear the debris from the road and stabalise the hill. Arborists were clearing trees at risk of falling at the site of Tuesday’s slip. A decision on when to reopen the rod was to be made on Wednesday evening.

‘‘The geology and varying terrain through the Mangamuka Gorge mean it will always be susceptible to some movement during severe weather, like what we’ve seen over the past 2-3 weeks,’’ NZTA said.

‘‘While the risk of major slips through the gorge has been significantly reduced by recently completed recovery works, the area remains susceptible to occasional, less severe slips due to the ground conditions in the Maungataniwha Range.’’

As ex-tropical Cyclone Tam bore down on the Far North earlier this month, many residents and transport officials were looking cautiously to the Mangamuka Gorge, hoping the highway repair job would hold up.

Tam dumped a month’s worth of rain and strong winds (up to 156km/h hurricane-strength winds were recorded at Cape Reinga on April 17) on areas of the Far North. Similar conditions caused State Highway One through the Mangamukas to close several times over recent years due to slips. The closures meant long detours for many and hit businesses hard.

Weekend storms brought a large slip cascade onto the road on the southern side of the hill again on Sunday.

That slip was cleared by Monday evening, but on Tuesday evening, in the middle of a third storm, another slip closed the road between Kitchen Rd and Makene Rd.

The recovery work was designed in a way that any future movement is expected to be much less severe, ensuring contractors can respond quickly and minimise disruption to the traveling public.

‘‘NZTA understands any closure of the gorge is disruptive, especially for freight, local businesses, and communities. Our contractors are working hard to minimise disruption and get the road reopened as soon as it is safe to do so.’’

Motorists can detour along State Highway 10, via Kāeo, or via Broadwood on the Kaitāia — Awaroa Rd.

This small slip, which did not impact the road, was the only real damage to the highway over Mangamuka Gorge, in the Far North, after a $240 million rebuild of the road.

NZTA reopened the troublesome stretch of State Highway 1 through the Mangamukas before Christmas 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.

The road was rebuilt over 22 months, with more than 1300 piles and 300 anchors installed, the road resurfaced, guardrails upgraded, and drainage improved.

At the peak of the Mangamuka work, about 75% of the workforce, and many of the suppliers, were from the Far North community.

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