Two And A Half Years After Cyclone Gabrielle, Here's How The Road To Piha Was Repaired

Scoop

9 hours ago

Explainer - The view is stunning - from high up in the Waitākere ranges, you can see all the way out east to downtown Auckland, the Sky Tower and the harbour, with Rangitoto Island visible on the horizon.
But until Cyclone Gabrielle and the storms of 2023 hit, this particular view did not exist at this spot on Scenic Drive.
Two and a half years ago, a wall of water, mud, trees and rocks smashed its way down onto the roadway, demolishing the road and carving a path 60 metres down the hill.
Now the road has been put back together again, but the view smashed out of the thick bush still shows off nature's power.
After close to three years of closure, the full road between West Auckland's Titirangi and Piha will finally reopen on Friday.
It has taken millions of dollars and the labour of hundreds of workers to get here.
This is just one of hundreds of slips and road repairs needed from Hawke's Bay to Northland following Cyclone Gabrielle and other weather events. In the complicated grunt work, analysis and problem solving, it is a good example of the mahi all around Aotearoa.
The process behind rebuilding a road is far more than just slapping some fill and asphalt down on holes.
"Water's a strange beast. It's unbelievable what it can do," said Auckland Transport (AT) road maintenance manager Johan Swanepoel as he surveyed some of the works along Scenic Drive.
This is the main road that thousands of Aucklanders and tourists from all over the world have taken out to Piha, one of the region's most scenic beaches. For nearly three years, anyone wanting to get to Piha, Karekare and other small communities out here have had to take long detours.
Here is how it has been restored.
Just how much road damage is there in Auckland, anyway?
More than 2000 slips on local roads were reported to Auckland Transport (AT) after the 2023 storms.
"We've only got about 70 left to fix," said AT director of infrastructure Murray Burt.
"Given the scale of the event, the complexity of some of the work, I think the team's done amazingly - and if you look across the country Auckland is well ahead of many parts of the country that were impacted by the storms at this time."
West Auckland was hit particularly hard, thanks to the wet and steep topography of the area home to the Waitākere Ranges Regional Park.
"We basically had damage on every piece of road we have in the West," Swanepoel said.
AT flood recovery programme director Jez Pellow said Auckland Council felt the strain of the unprecedented widespread damage.
"It pushed it to the absolute limit. I mean, I've lived in New Zealand for 18 years, I've never seen anything like this before.
"We had, in certain parts of the region, one-in-200-year rain events ... So, you know, for instance, stormwater infrastructure, public and private, completely overwhelmed, all of them. They don't have a design life to cope with those types of events."
In the west Auckland area, AT said 191 complex slips needed repairing: 119 minor (less than $250,000 to repair) and 72 major (more than $250,000 to repair). Earlier this year AT said the work was 80 percent complete.
AT said the goal now is to have the very last of the Auckland cyclone repairs done by April 2026.
"We'll still come in ahead of schedule," Pellow said. "We were anticipating this could have taken four or five years and we'll get to a point where the works on the road network will be completed by 30th of April next year."
What kind of damage is there on the roads?
There are several ways roads can be affected by severe weather. There is surface flooding and then there is subsidence, when a road sinks due to too much water in the ground and weak underlying soil or rock.
In the Waitākere ranges, there are a lot of overslips and underslips.
Overslips are when plants, soil, rock and other debris falls onto a road from above. Underslips are when the downhill side of the road begins to give way.
Underslips are often more complicated to fix as they can require entirely rebuilding the road.
Some of the biggest projects on Scenic Drive have been repairing giant underslips where nature gouged out huge chunks of infrastructure.
"We initially prioritised repairing those areas that were impairing people's access to their properties," Burt said.
Where do you even start with repairing a road like the road to Piha?
The first step is clearing out the immediate debris and hazards on roads and possibly dealing with utilities like power, gas and water lines, but then the invisible work of analysing the ground begins and can take some time. No two slips are exactly alike.
"We normally look at three to four options of how we will repair and then a decision is made how the repair will happen," Swanepoel said.
AT has been able to work with existing contractors from Ventia, Fulton Hogan, Liveable Streets and Downer as well as working closely with NZ Transport Agency Waka Kotahi and the government for funding.
After the 2023 storms, there were 10 large slips on Scenic Drive between Titirangi village and the turnoff to Piha.
Several slips collapsed the busy stretch of roadway between the Titirangi roundabout and Woodlands Park Drive, which was reduced to stop-go travel and then closed entirely while huge new retaining walls rebuilt huge chunks of Scenic Drive that had slid down the hillside.
That section reopened in December.
"A design is then done and that takes quite a lot of time to do all of that and that's one of the reasons why it takes a year and a half to do this kind of work for this section.
"We try to build back better," Swanepoel said. "This needs to last 100 years."
The second part of the work has taken in several more large slips on the winding rural section of Scenic Drive that heads out towards Piha.
There are still a few smaller projects on Scenic Drive that will require some temporary stop-go closures in one lane, but otherwise the road itself will be fully open for the first time since 2023.
How the road is repaired
Much of the work can be compared to an enormous sewing project, only with gigantic beams and anchors being inserted deep into bedrock and hillsides to keep fragile land together.
RNZ stood with a team of AT staff at "Scenic 6", the final massive repair job where the newly opened view across Auckland stands at the top of a 60m-drop.
"This is our final site that we had to deal with," Swanepoel said. "Basically what has happened here is this side of the road collapsed into the valley. If you look down here, it's about 60 metres deep. Half of the road was gone."
Much of the repair work will be invisible to drivers soon humming along on Scenic Drive, but that's the idea. The road rests on a concrete piled, tied-back wall and under the road surface are concrete slabs to raise it back to the former level.
"This looked like a mine," Swanepoel said of one massive underslip.
"We had to basically build the whole road back ... We've had to bring it up from the bottom."
Another section of road looks almost like it was never damaged, but appearances are deceiving.
"This is a deep fill," Swanepoel said, standing on the resealed road. "This is like two diggers deep, if you can say it that way."
Walls built under roads or retaining walls help shore up the stability.
Enormous piles of concrete or metal - sometimes up to 20m long - are driven deep into the earth, while anchors and soil nails - which are exactly what they sound like - are also used.
The anchors and nails are also several metres long depending on the site conditions. The resulting lattice-like effect reinforces the ground beneath.
A variety of draining solutions were also employed at sites to ensure water can escape in another heavy rain situation.
"We strive to get the best out of what we can afford," Swanepoel said. "For us this bit here will not slip again."
Ultimately, the goal is to hold the land together and facilitate drainage.
"These are tried and tested engineering solutions, but it's basic grunty stuff, you know, building lots of walls," Pellow said.
"When you drive past that nobody can see it. There's a massive piece of engineering that as you say, it is literally stapled into the side of the earth, and you wouldn't even see it."
Okay, but why does it all take so long?
There are several reasons these projects are taking years to complete. There is the time it takes for geoengineers to study the site, to ensure it is safe to work on and to figure out the best solution.
Because of the damage to so many roads around West Auckland, projects have had to be staggered to avoid access being cut off by multiple closures at once.
"We could have closed the whole road, we could have worked on all 10 at the same time," Pellow said. "But what that would have done is that would have been completely destroyed access for those communities."
And sometimes it gets more complex. Estimated deadlines for the work to end have moved a few times.
While working on two slips on Scenic Drive between Titirangi village and Woodlands Park Road, a third slip was discovered, and there was also the constant threat of more overslips from the hills above.
"I think a lot of people don't really realise that sometimes it's just not possible to predict everything from the start," Swanepoel said.
How much has all this cost, anyway?
The AT Flood Recovery Programme is estimated to cost $390 million, jointly funded by the Crown and Auckland Council: NZ Transport Agency Waka Kotahi ($199m), Auckland Council ($81m) and Crown Infrastructure Partners, now National Infrastructure Funding and Financing ($110m).
Documents AT provided to RNZ show the Scenic Drive repairs at eight sites have cost $15.8 million, with some drainage work still to come.
Overall the government has provided $2.9 billion for North Island weather events response and recovery since 2023, with Transport Minister Chris Bishop announcing extra funding for roads in May's Budget.
What about the people affected by this disruption?
For close to three years, thousands of people living out in West Auckland have been living with the floods and cyclone aftermath.
"Understandably, people, they want to get back to some sort of sense of normality," Pellow said. "Businesses have been affected, people who are just trying to go about their day-to-day business have been affected, and we are acutely aware of that."
Rahul Uppal, owner of the Olive Kitchen & Bar on Scenic Drive just before the closed section, called the road reopening "a huge milestone".
"I've waited three years for this moment - and to be honest, it's felt more like a decade. We faced challenges that nearly forced us to close our doors, but our locals kept us going. If this were anywhere else in the world, we might have been long gone - so we're truly grateful to our community."
Uppal said the restaurant, which just marked its sixth anniversary, has been hit hard by first the pandemic and then weather chaos.
"We hope people from across Auckland will take the beautiful drive out to Titirangi and Piha, support local businesses, and help us rebuild after these challenging years."
Will this work actually hold up to future storms?
AT staff emphasise there is no foolproof protection against all future weather damage, particularly with the uncertainties caused by climate change.
"There'll always be slips on the network," Pellow said. "I think due to the nature of how our roads are engineered, particularly places like the Waitākeres and the geology of that place and also the significant rainfall that we experience. There's always going to be vulnerabilities there."
But in heavy storms since, the work has held up so far.
"In July, we had significant rainfall and all of the walls, all the retaining structures and the drainage that we've built as a consequence of 2023 has stood up," Pellow said. "None of them have failed. So that gave us a lot of reassurance."
AT is trialling new electronic early flood warning systems at three flood-prone sites and is developing a landslide predicting framework using data from existing landslides and AI (artificial intelligence) mapping across almost 8000km of Auckland's local road network.
Burt said with the hazard mapping, "we've overlain the slope angles understanding the underlying geology and geotechnical parameters, and using AI we've been able to come up with a landslide hazard map for all of the roads" in Auckland.
At some sites, inclinometers have been buried under the road - tiny devices that measure slope stability and can warn if the road is slipping under the asphalt.
"We've learned a hell of a lot," Pellow said. "What we've been able to do, for instance, is we've taken the data and the actual real life slips across the network, and we've used that to extrapolate that out across the whole road network, we've actually identified where the vulnerabilities are, where the slip hazards are."
"I think we've learned that the Auckland road network is quite vulnerable to these type of events," Burt said. "With climate change we're going to see more weather events quite frequently.
"I've been involved in humanitarian and disaster response all around the world, and I do think that the way Auckland responded to this was pretty good ... Overall, as a city and a country we should be proud of where we've got."