Cost to fix Northland landslide estimated at more than $10m

Repairs to the Helena Bay Hill landslide in Northland could cost more than $10 million, with a Northland transport leader warning the work must proceed as quickly as possible to prevent the road beneath it from collapsing.

By Susan Botting of Local Democracy Reporting

More than 200,000 tonnes of material came down onto Russell Rd overnight on Wednesday, January 21, cutting the main southern access to the storm‑hit Whangaruru coast, which remained under a Civil Defence state of emergency.

Northland Regional Transport Committee chair Joe Carr said repairs must be urgent to stop the roughly 100m stretch of Russell Rd buried under the slip from giving way.

He said the longer the slip’s more than 100,000 cubic metres of clay, boulders and vegetation stayed in place, the higher the collapse risk.

“We’re at risk of losing the road,” said Carr, who is also a Northland Regional Council councillor and former Far North District Council roading committee chair.

“If that road gave way, where would a new Russell Rd route go? There’s nowhere else to go.”

Carr said the distance of slip-covered road might appear short in length, but the landslide’s sheer mass – more than 200,000 tonnes – made it extremely dangerous.

“That’s a fair weight,” he said.

“We don’t want to end up with an underslip and the road falling away. Underslips are way more complex to fix.”

Carr said the slip needed to be fixed as quickly, effectively and economically as possible.

The landslide covered more than a hectare and was still moving.

The Regional Transport Committee, a powerful statutory roading body made up largely of local councils, was closely monitoring the threat due to the strategic importance of Russell Rd.

The Helena Bay Hill landslide is comparable in many ways to other major Northland slips, including the Brynderwyns, the Mangamukas, the Mid North’s Lemon’s Hill collapse, and another major slip at Helena Bay.

All shut key access routes for months and required multimillion‑dollar repair programmes.

Whangārei District Council infrastructure committee chair Brad Flower said those working on the project were acutely aware of the risk the slip posed to the road underneath.

He said the council and its partners were moving at pace, but the job could not be done well without thorough preparation.

“It’s all about the six P’s – prior planning prevents piss‑poor performance,” Flower said.

He said the planning work underway now would translate into more efficient on‑the‑ground repairs.

Flower said fixing the slip would likely cost “upwards of $10 million”, with costs still being finalised before going to the Government for funding.

The first physical work had begun, with crews preparing a dump site on a farm about 2km back along Russell Rd toward Whangārei. The site could take all the slip debris if required.

Forty‑tonne dump trucks would be used to shift debris to the inland dump site.

Flower said transport would need to be done carefully because of a smaller underslip on the road not far above the main landslide.

Investigations were also underway with the local community on the seaward side of the slip to find a second dump site, allowing debris to be removed simultaneously from both sides using smaller 10‑tonne trucks.

Major earthmoving contractors who worked on the award‑winning Brynderwyns recovery have been brought in to tackle the Helena Bay Hill landslide. Fulton Hogan, the lead contractor, has also sought input from other civil construction firms interested in joining the project.

Flower said some of the 100‑tonne rocks in the slip could not simply be rolled down the hill.

“Who knows where they might stop?” he said.

Instead, they would be broken up with rock crackers or, if necessary, blasted in a controlled manner to ensure only the rock was affected.

He said the Helena Bay Hill landslide was larger in volume than the Mauao/Mt Maunganui slip that hit the campground on January 22, less than 24 hours later, but the impacts were very different.

“Our hearts go out to them,” Flower said.

Whangārei District Council Hikurangi‑Coastal ward councillor Steve “Tractor” Martin said Northland was extremely lucky the Helena Bay Hill collapse occurred during the night.

“We are really lucky it happened when it did – that there were no cars driving under any of the slip’s giant rocks,” Martin said.

“Just imagine if a family had been driving along Russell Rd when the slip came down.”

Martini said people must not underestimate the scale of the landslide.

It covered an area roughly the size of a rugby field.

“What’s at the bottom on the road is just like a pimple on a pumpkin compared with the whole thing,” Martin said.

Martin visited the top of the slip on January 25 and said new 100m long, “higgledy‑piggledy” cracks had opened up from west to east.

“These scream instability.”

He said people had planned to sleep overnight in the Ōakura Hall ahead of an event the morning after the slip crashed through its back wall on January 18.

That timing, he said, likely saved lives.

– LDR is local body journalism co-funded by RNZ and NZ On Air.