The Waikura underslip along SH35, pictured on Sunday. Rain on Tuesday caused more material to fall. Inset: NZ Transport Agency Waka Kotahi incident controller Richard Bayley spoke with the Gisborne Herald about work on SH35. Photos / NZTA
The Waikura underslip along SH35, pictured on Sunday. Rain on Tuesday caused more material to fall. Inset: NZ Transport Agency Waka Kotahi incident controller Richard Bayley spoke with the Gisborne Herald about work on SH35. Photos / NZTA
Road crews are working hard on State Highway 35 in the northern parts of Tairāwhiti, clearing slips and excavating soil following severe weather last month.
The road remains closed between Wharekahika/Hicks Bay and Pōtaka after more land movement in the area this week, according to the latest information from NZTransport Agency Waka Kotahi (NZTA).
The Gisborne Herald spoke with NZTA incident controller Richard Bayley this week about how recovery work is going and the biggest challenges involved.
Good progress is being made at the largest of the slip sites along State Highway 35, but the weather has continued to expose the fragility of the landscape.
NZTA says the Waikura underslip, between Pōtaka and Wharekahika/Hicks Bay, was its main focus and more ground had fallen away during rain on Tuesday.
Elsewhere, the Punaruku slip north of Te Araroa is almost 250,000 metres of material – half the estimated total amount of debris to have fallen along the highway.
NZTA incident controller Richard Bayley said the land movement at the Waikura underslip showed how “fragile” the entire stretch of SH35 was and how dependent it was on the weather.
Biggest challenge of the clean-up
When asked what the most difficult engineering challenge of the clean-up was, Bayley referred to the Punaruku slip.
“We’ve got a temporary access track that is connected through and across it, but it is literally just a dirt track at the moment.
“With the rain, it’s completely inaccessible to any vehicle, even 4WD. Unless you’ve got a tracked machine, you can’t get across it.
“We’re working to shore that up over the next, probably week really, with some aggregate to make it a state that would be accessible to the public.”
NZTA intended to “retreat” the road for the “complex” underslip near Pōtaka, which meant realigning the road away from the slip.
“Apart from that, a lot of it is fairly straightforward slip removal, slip clean-ups and debris removal from the road, cleaning out drainage systems, all that sort of stuff.”
Monitoring of the Punaruku slip site
The Gisborne Herald asked if NZTA had identified the Punaruku slip site as a risk point before the weather event last month.
“We were aware of the potential for some instability on that section of the network. Large-scale landslides like that one in particular, and like some of the ones we see in Waioweka Gorge, are very hard to predict.
“If we happen to have monitoring equipment on them at the time, we can sometimes pick up some early signs.
“The level of rain that we had up there, and the intensity of it, often exceeds some of the modelling that you do from an engineering perspective, so those large-scale landslides are extremely hard to predict when and where they will occur.”
Bayley said it was often easier to see the signs of smaller-scale slips, but it could be difficult with bush-covered hills.
NZTA proactively monitored some sites around the country and was investigating whether monitoring equipment would be effective to implement at Punaruku.
“We have others with [State Highway] 35 that we are monitoring, such as the slip that started moving ... I think it was [in] 2022 at Makorori.
“We do have some monitoring equipment out there on the network already, so it’s not too big of a stretch to add in sites like this, but it is quite complex equipment that comes with a cost.”
Further damage to the Waikura underslip on SH35, pictured on Tuesday after rain. Photo / NZTA
Isolated communities
Several communities along SH35 were completely cut off from one another and the rest of the region in the immediate aftermath of the severe weather event last month.
From a state highway road network perspective, Wharekahika/Hicks Bay was the only community that remained isolated as of this week.
Bayley said NZTA was facilitating movement through there via Civil Defence.
“But, on [Tuesday] for example, our report back from the early morning inspection was that the surface was very slippery.
“Even in 4WDs, the guys were reporting that there’s a lack of traction, even going at slow speeds, because of the amount of mud that has made its way on to the highway.”
When asked how people had treated his staff, Bayley said “generally pretty well”.
“There’s always a little bit of frustration and anxiety out there during these events, especially when we aren’t always able to provide strong dates and times when access will be re-established in the early stages.
“What we do notice is that in those really early days, post-event, anxieties are high. There are a lot of unknowns out there and people are trying to plan for supplies and the likes, and it gets pretty frustrating.
“On our side, our workers out there are doing some pretty long hours to try and get the road open.”
Cost of clean-up and how much debris is being moved
Bayley said there were no robust numbers available at this stage for how much the clean-up would cost, but NZTA was working on getting that information.
While 500,000cu m was the initial estimate for the debris that fell along the highway, Bayley said NZTA did not expect to move the majority of it.
Around 20,000 to 40,000cu m had been “actively moved” so far, he said.
A truckload is about 5-6cu m; the equivalent of about 4000 to 8000 truckloads of material had been moved.
Bayley said clearing the road completely would take “a number of months” and the challenge was to get the road into as good a shape as possible before winter.
“Some sites could be potentially more than a year or a couple of years for some of the more complex sites, but there’s a very small handful of those, which includes the Punaruku slip.
“We’ve got some other slips we’ve identified that are a bit more complex as well.
“We are expecting the momentum that we’ve got at the moment with the contractors to continue and we’ll be going straight in without any delays into some of the smaller recovery works, while we work on the more complex sites in the background.”
