Former roading contractor Keith Taylor, who spent his life working on Northland roads before his retirement, said the ground was “unstable”.

“There’s one good reason why that road was never touched over the years when they did all that work on the north side.

“They didn’t do work on the south side for precisely the reason that’s happening now.

“It’s unstable ground.

“Whenever you do any work you have to allow for ground movement when you finish.

“You can’t do that on a hill like that because of the huge amount of soil above it.

“They’d be better off putting in a new road.”

Taylor said the Brynderwyns was a “very tricky hill, exactly the same as the Mangamukas”. State Highway 1 at the Mangamukas is set to reopen by Christmas after a two-year closure.

“When dealing with unstable ground, you have to flatten out the batters [angle of the hill above the road].

“It’s awkward because of the sheer height of it.

“Once you disturb something like that … it’s like having sand and tipping water into it.

“If you don’t tip water into it, it’ll stay in a heap.”

Taylor’s comments are backed up by an independent geotech report released in May following April slips that were caught on video, showing a large chunk of hillside and trees falling onto the road below.

The report said the combination of soils and rock that gave way was so unusually slippery, the area was in a “critical state of stability”.

“It is also clear from the video, and observing the material involved in the slip, that this area of the slope was in a critical state of stability, where any disturbance was highly likely to trigger movement,” the report by engineering firm Tonkin and Taylor said.

The report suggested the project was not yet out of the woods and recommended investigating for any further “uncemented” soils that could present a wider risk.

However, NZTA decided to take an “observational approach”.

One Northlander who drove through the latest slip site, did not feel safe doing so.

Kerikeri resident Chloe Whitehead returned home through the Brynderwyns on Sunday following a trip to Auckland.

She hit the Brynderwyns about midday and admitted she felt “a bit nervous”.

“You could see a couple of slips and quite a few uprooted trees that were leaning down.

“It didn’t look like it’d take much for them to come down.

“It doesn’t look like it’ll last long again.”

Whitehead said while she was pleased the Brynderwyns were open because it reduced her travel time, it was “best not to have it open”.

“I was happy it was open because it cut off 30 minutes, but some parts didn’t look ready, especially where the trees had fallen down.

“If there was more rain, which there was, it could have fallen right down again onto the road.”

Pressure has been mounting for an alternative, four-lane highway since the initial series of Brynderwyns closures in 2023 when a cluster of severe weather events hit the region, including Cyclone Gabrielle.

That intensified this year, when the initial nine-week closure to repair the damage dragged out to four months.

Northland Chamber of Commerce president Tim Robinson was worried the repeated closures would put people off coming to Northland.

Robinson said he was “deeply concerned about overarching perception it’s creating”.

“People are going ‘It’s too hard, I can’t be sure the road will be open, we’ll choose to do business somewhere else’.

“They’ll go on a holiday or short break somewhere else, because they’ll be worried if Northland’s main road will be closed or they might get stuck altogether.”

Robinson said overall, the Chamber was “thoroughly disappointed”.

“When you put into the mix the cost of living crisis, the lights going out and Transpower’s incompetence, we’ve got a perfect storm.

“The business community is really doing it hard. That’s why we’re seeing a growing number of businesses failing.”

Northland MP Grant McCallum understood some drivers were nervous about the stretch of state highway but reassured them it was safe.

“Ultimately we are relying on the geotech experts.

“If it wasn’t safe they would have shut it.

“It’s a fragile piece of land, we all know that.

“If we hadn’t spent the money … we really ran the risk of having catastrophic failure and having the road out for months and months.”

NZTA project director Mark Ware said: “Extreme rain will always cause some movement in the hill”.

“We’re actively monitoring these movements.

“As part of the work undertaken during the rebuild of this section of SH1, we’ve installed electronic monitoring in the hill to alert us to movement – and when there is movement in the hill, we have a crew assigned to manually watch for changes.

“We also have crews on standby to clear the road if material does come down, and the extra space built next to the lanes during the recent recovery work means it is easier to clear slips quickly and re-open the highway for road users.”

Transport Minister Simeon Brown said the coalition Government “recognises Northlanders need a more resilient route than the Brynderwyns can provide”.

“We will make good on our promises to the people of Northland.

“As announced previously, NZTA intends to approach the Northland Roads of National Significance as a single strategic corridor, with Warkworth to Wellsford the first section being focussed on.

“We are committed to constructing an alternative to the Brynderwyns and will investigate all options, including private finance, to accelerate its construction.”

However, Brown did not provide a specific timeline for this.

Earlier this year, he said an alternative to the Brynderwyns would be built within 10 years, if not sooner.

What makes the Brynderwyns so challenging?

GNS Science landslide duty officer Brenda Rosser said the Brynderwyn Hills were dominated by “greywacke” a type of sedimentary rock that makes up the main mountain ranges in New Zealand.

“Over time, tectonic land movement and weathering have deformed and weakened the rock, leaving it loose, crushed and sheared in places.

“Further, in places the terrain is steep.

“These conditions increase the likelihood of landslides from earthquakes and heavy rainfall events, particularly where the rock is highly weathered and uncemented or loose.”

Rosser said as New Zealand is a hilly country with high rainfall and frequent earthquakes, “landslides are an ever-present hazard in many parts of the country, with climate change likely to increase the risk of landslide events.”

Jenny Ling is a news reporter and features writer for the Northern Advocate. She has a special interest in covering roading, lifestyle, business, and animal welfare issues.