Safety and resilience improvements while SH1 is closed by slip


Waka Kotahi NZ Transport Agency is making the most of the closure of State Highway 1 through the Mangamuka Gorge to carry out extensive maintenance and repairs.

SH1 has been closed between Victoria Valley Road and Makene Road since heavy rain caused slips and widespread flooding across Northland in mid July.

A single slip is keeping SH1 closed to all traffic, but Waka Kotahi Northland System Manager Jacqui Hori-Hoult says the road could be open to one lane for light vehicles by late October, depending on the weather

A contract has been awarded to Fulton Hogan as lead contractor to manage construction of a wall of concrete piles across the slip face on the road’s current centre line. The piles will support the road where six to seven thousand cubic metres of rock and soil have fallen away, undermining the road.

Local hapū and iwi have held a karakia at the slip site for the safety of workers and contractors who are setting up to start work next week. The area, also known as Maungataniwha, has great significance to many iwi/hapū in the north.

Meanwhile, SH1 through the gorge has been getting some special maintenance attention.

“While the road is closed maintenance crews have been hard at work, repairing the road, replacing roadside guard rails, drainage maintenance and generally tidying up the roadside. Usually we would have to close the road or have stop/go traffic managers in place to do this work safely or we would schedule it around resealing and other work.”

“Waka Kotahi is very pleased to use this opportunity to make safety and resilience improvements. Motorists will certainly notice the difference when the road reopens.”

Road crews repair guard rails and make other roadside improvements while SH1 through the Mangamuka gorge is closed by a slip.

Ms Hori Hoult says construction of the supporting wall is the first phase of work to reopen the road to two lanes. That first phase will take at least six to eight weeks depending on the weather.

“We’re dealing with a very challenging and complex slip in a difficult environment. As well as repairing the slip below the road, we have to consider the options for restoring the road to two lanes. We can rebuild all of the road that’s been lost or cut into the hillside with a new alignment. Our team is in that process at the moment.”

In planning the repair and maintenance work, Waka Kotahi has the safety of road crews as its top priority.

“We’ve found the ground is unstable both under and above the road and the concern remains that any repair work could reactivate old landslips.”

“The instability of the slip area has even caused us to close the road at times to the maintenance crews. It just wasn’t safe to move vehicles and equipment past the slip.”

“There’s been a lot of rain this winter, but as the weather improves and the days become longer, we’re looking to progress the slip repair so we can get the road open.”

Until SH1 reopens, the recommended detour route is SH10 with motorists advised to allow an extra 20-30 minutes for the journey.

Waka Kotahi acknowledges the disruption to the local community and the extra time and cost of having to travel on SH10.

We thank motorists for their patience and understanding. We're working as quickly as possible in difficult conditions to repair and reopen the road.

Road crews repair guard rails and make other roadside improvements while SH1 through the Mangamuka gorge is closed by a slip.

Leading the karakia at the Mangamuka Gorge are kaumatua (left to right) Bishop Te Kitohi Pikaahu, Te Pīhopatanga o Te Tai Tokerau and Raymond Harris, rangatira of the Mangamuka hapū (Ngāpuhi).

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