Excavators at work on the ridgeline above Kauri Tree Corner, where two fresh slips stymied plans to reopen State Highway 1 over the Brynderwyns this week.
Photo: NZTA / Waka Kotahi

The re-opening of State Highway 1 over the Brynderwyns has been pushed back to the end of June – adding another seven weeks to what was supposed to be a nine-week closure.

The highway had been due to reopen on 13 May after extensive slip repairs and road strengthening on the south side of the Brynderwyn Hills.

However, those plans were scuttled by two new slips on 26 and 30 April.

NZ Transport Agency Waka Kotahi infrastructure delivery manager Mark Kinvig said the project had been on track until that point.

He said the agency was aware how difficult the highway closure was for Northland businesses and communities.

“Our priority has been to undertake geotechnical and safety assessments to determine the best option for stabilising the hillside and getting State Highway 1 Brynderwyn Hills open as quickly as possible,” Kinvig said.

“While our plan is to reopen at the end of June, if there’s a significant amount of unexpected rain, or further instability is found, that could delay the reopening timing.”

NZTA remained committed to completing the work as quickly as possible to ensure a safe and reliable road over the Brynderwyns in the short to medium term, he said.

Digger operators were working from a platform at the top of the slips, removing soil from the ridgeline to reduce the risk of further slips.

That would allow fallen soil and trees to be safely removed from the bottom of the slips.

Kinvig said the team was working seven days a week, weather permitting, to remove up to 55,000 cubic metres of earth at Kauri Tree Corner, where the slips occurred.

“We are maximising the number of trucks, diggers and workers on site to ensure the soil removal is a continuous operation, utilising daylight hours, to get it clear.

“We have built in contingency for poor weather, however the ground conditions remain unstable and continue to be actively monitored by staff and GPS sensors. There is a risk of further slips until we complete the stabilisation works.”

Three detours are in place for traffic between Northland and Auckland.

The east coast route, via Waipū’s Cove Road, is for light traffic.

Paparoa-Oakleigh Road, just west of the Brynderwyns, is open to all traffic except heavy trucks in the HPMV (high productivity motor vehicle) class.

HPMVs have to use State Highways 12 and 14 around the west coast.

Even once the repairs to SH1 over the Brynderwyns are complete, the road is expected to last only another seven to 10 years.

The coalition government has committed to building a new, four-lane highway around the Brynderwyns within 10 years.

Meanwhile, work is continuing on the other section of SH1 in Northland closed by major storm damage.

The highway through Mangamuka Gorge, south of Kaitāia, closed in August 2022 and is expected to reopen by the end of this year.