The detour through Waipū and Mangawhai to bypass the State Highway One blockage at Brynderwyns could have both lanes reopened on Friday, but heavy trucks will still have to use the SH12/SH14 detour.

The road was the main detour around the Brynderwyns – which was blocked due to slips caused by heavy rain earlier this year – but was closed on Friday due to numerous slips and floods caused by the 370mm of rain in the area in 24 hours.

Fortunately, work on the Brynderwyns is still tracking well, Waka Kotahi said, although rain over the weekend caused some small slips. The road is still on track to fully reopen in late March, with controlled access earlier.

Cove Rd from Mangawhai to Waipū is not currently available as a detour route due to the Langs Beach bridge being closed. It remains open at either end but cannot be used as a through road.

Opening of the Langs Beach bridge has now been delayed after contractors found the soil was more saturated than expected and they had to excavate and backfill more than initially thought.

Northland Transportation Alliance maintenance and operations manager Bernard Petersen said they now intended to have the bridge open by Wednesday morning.

“We realise people have been looking forward to it happening sooner and we’re sorry for the additional day of this impact on their lives.”

The Langs Beach bridge was assessed by a structural engineer and while there is no damage to the bridge structure, the abutments had been washed out and contractors have been working on backfilling these.

Pedestrians are also advised to not use it due to risk of pavement collapse. A slip near King Rd on the Mangawhai side will be cleared once Northpower has completed relocation of a high-voltage power line.

Saturated soils have also slowed repair work on the underslip on the Kaiwaka-Mangawhai Road near the Hilltop Road intersection, Petersen said. It would reopen on Friday rather than midweek as initially expected.

This section of the road, as well as the Langs Beach bridge, would reopen with unsealed surfaces, which would be easier to maintain in the short term.

At this stage, the likely date for full reopening of the official SH1 Brynderwyn detour route for light vehicles through Mangawhai and Waipū is Friday.

There were a number of sites of concern on Cove Rd, Petersen said, mainly where the road shoulder had been washed out and the road surface undermined.

When it does reopen, the restriction to prevent use by truck and trailer units, as directed by the Northland CDEM, will remain and will continue to be supported by police patrols.

Authorities in Northland are advising travellers to stay up-to-date and amend their plans if necessary as key local roads damaged in Friday’s heavy rain around Mangawhai and surrounding areas will remain closed until midweek and in some cases, longer.

“Friday’s downpours over Mangawhai and the surrounding area have caused significant damage and despite the contractors giving it their all over the weekend, the options are still quite limited,” Northland Civil Defence Emergency Management (CDEM) Group Controller Graeme MacDonald said.

“We know there are many people who live and work around the Mangawhai and surrounding area whose normal routes will not be available, as well as the freight industry and visitors to our region. By midweek, we expect to have a better set of options around this area; however, it will be Friday before the full reopening of the official SH1 Brynderwyn detour route for light vehicles through Mangawhai and Waipū.

“Until then, unfortunately, all parties are going to have to continue to compromise. The damage to those roads has been significant and we appreciate all the work that’s been put in over the weekend, including the restoration of SH1 at Topuni by Waka Kotahi NZ Transport Agency – Northland overnight by Saturday morning.”

Meanwhile, state highway access in and out of Northland while SH1 Brynderwyns remains closed to all traffic and the detour routes for all traffic between Auckland and Northland are SH12/14 via Dargaville – recommended route for all heavy traffic – and Paparoa/Oakleigh Rd for lighter vehicles. A temporary 70km/h speed limit is in place on the road.

Access in and out of Mangawhai is for local residents/workers and local freight deliveries only – Mangawhai Rd off SH1 near Te Hana is the only access point into Mangawhai today. There is still one single-lane section of this road past an underslip and there are concerns about further deterioration of this.

Kaipara District Council and roading partner the Northland Transportation Alliance are asking that only local traffic – people who live or work in Mangawhai – and local freight deliveries use this route to get in and out of Mangawhai.

Other through-routes (unsealed local roads) between Kaipara and Whangārei districts are also restricted or closed. Waipū Gorge Rd is closed due to a slip during Cyclone Gabrielle – Finlayson Brook Rd is closed by a dropout/underslip.

Devich Rd remains closed at the bridge due to safety risks. Access is available out both ends.