SH1 through Mangamuka Gorge to be open for Christmas

4 MinutesBy NZ Trucking magazineOctober 20, 2020

The NZ Transport Agency expects to open State Highway 1 through the Mangamuka Gorge in the Far North to a single lane of traffic over the Christmas holiday period.

The road will be open to light vehicles under stop/go traffic management, but it will still be some time before trucks and buses can travel the road, says NZTA Northland system manager Jacqui Hori-Hoult.

The road has been closed since heavy rain across Northland in mid July brought down eight slips in the gorge. Most of the road has been cleared to at least one lane, but there‘s been no safe way past the biggest slip on the northern side of the gorge.

“Initially the plan was to open the road in late October by installing a wall of concrete piles to support the road, but the slip repair is complicated with significant safety issues.”

“An estimated 7000 cubic metres of material fell away beneath the road, leaving the road surface unsupported to the centre line. The earth beneath the road is brittle and unstable and there is an old slip above the road that could reactivate.”

“Due to the instability of the slip site, we have to put in small temporary piles to make sure the road can safely support the large machinery required to install the permanent piles, which will be 15 to 20 metres long.”

NZTA is aiming to achieve that and open the road to light vehicles in mid December.

“Our crews will be working 20 hours per day to get this done as quickly as possible, but much will depend on the weather and the stability of the hillside. We‘ll keep the local community informed of progress and a likely opening date.”

The cost of this first stage of the repair is estimated at $3.8 million.

Works will shut down for three weeks over the Christmas/New Year period to accommodate holiday traffic. Traffic management will be in place throughout this period.

Hori-Hoult says that in the New Year the road will be closed again so the works team can cut into the hillside to realign the road as a permanent solution.

“We‘re still working out whether we can do this work and have the road open at the same time. The team is aware of the impact the road closure has on our local communities.” 

“NZTA acknowledges that closing the road means extra time and cost for people to travel on the recommended detour route – SH10 – which can add 20-30 minutes to the journey.”

The area, also known as Maungataniwha, has great significance to many iwi/hapu in the north and NZTA is consulting closely with them on the work under way and on the permanent repair. 

Maintenance crews have taken advantage of the road‘s closure to do extensive work, repairing the road surface, replacing roadside guard rails, drainage maintenance and generally tidying up the roadside.

“We thank motorists for their patience and understanding. We‘re working as quickly as possible in difficult conditions to reopen the road. Achieving that, even just for the holiday period, will be our Christmas present to people in the Far North.”