State Highway 1 to Kaitaia opens a year after devastating Northland floods
Wednesday, 30 June 2021
One year after Northland’s one-in-500-year storm event closed State Highway 1 at Mangamuka Gorge, the community is waiting with bated breath for the road to reopen.
Waka Kotahi NZ Transport Agency has spent $16.2 million on fixing the main road north to Kaitaia, which was closed by eight slips from the floods on July 17, 2020.
From 6pm on Wednesday, the route will open to all vehicles except those over-dimension, said Jacqui Hori-Hoult, regional manager Te Tai Tokerau me Tāmaki Makaurau.
At the largest slip – known as slip eight – traffic will still be reduced to one lane so workers have enough space to finish the largest retaining wall, which is 135m long and 4m high.
**READ MORE:
* Main road to Far North to close again for slip repairs after brief opening over Christmas
* Northland floods: Road to Kaitaia to open for Christmas, five months after slips
* Northland flooding: Mangamuka community 'cut in half' as road closure drags on
**
The road closure has caused significant disruption to the Far North community, with the small community of Mangamuka cut in half.
For those living south of the slips, the drive time to Kaitaia doubled from 30 minutes each way to an hour.
The closure has also impacted the Bay of Islands and Doubtless Bay communities on the alternate route north, State Highway 10, which has been marred by congestion and crashes.
For Mangamuka Dairy owner Eliza Kete, the official opening is a bit of an anti-climax.
“It’s going to be great that it’s going to be open, but because we’ve waited such a long time we’re not overly excited now.”
On Tuesday afternoon, Kete had not had any official word about what time the road would open on Wednesday.
“We’ll just wait and see, and hope it all goes well.”
The road closure has seen business drop by at least 30 per cent, which is a big impact for a dairy already impacted by the lack of tourists due to Covid-19.
Kete said she hopes a big boom in business will follow the opening, to make up for what she has lost in the last year.
Hori-Hoult acknowledged the closure has been an inconvenience.
“To our communities and Te Tai Tokerau, I want to really thank you for your patience while our team has been on here, working as fast, as efficient and as safe as we possibly can to be able to open.”
Given the importance of the route, the work has not only included repairs but drainage to limit damage from any future weather events, she said.
Nearly 200 people have worked on the project in the last year, with the costs escalating from $3.8m for the first stage of the repairs, to an estimate of $13.8m last year, to a final cost of $16.2m.
Eight slips were identified, with slip eight in imminent danger of causing the road to entirely fall away nearly 150m to the river below, Hori-Hoult said.
“It was under tough conditions that our team took on the challenge to restore this important connection. As they worked, they needed to continually monitor the hillside to ensure there was no new earth movement.”
Slip eight needed significant strengthening work, with a slips both above and below the road.
Nearly 50 concrete and steel piles were inserted into the hillside to stabilise and support the road below, and the same number inserted into the hill on the other side of the road, as part of a retaining wall to prevent the earth above from slipping down.
A total of 800 cubic metres of concrete was poured at site eight – 134 concrete trucks’ worth.
Hori-Hoult said the retaining wall will help future-proof this section of state highway.
“While site eight was the most complex, each of the damaged areas have presented different challenges, with work often being carried out in narrow corridors or on steep terrain.”
Work has been done to ensure the new infrastructure fits in the environment, by choosing natural colours for the retaining walls and using native, locally sourced shrubs for replanting work.
The retaining wall at slip eight will have a design created by local iwi, Ngāti Kahu, then will be sprayed with anti-graffiti material.
Mangamuka Gorge facts:
More than 200mm of rain fell over 10 hours on July 17, 2020.
Almost 8000 cubic metres of dirt fell away from slips seven and eight.
Nearly 200 people worked on the project.
Five retaining walls were built, the largest being 135m long and 4m high.
About 1300 vehicles a day normally use SH1 through Mangamuka Gorge.