Queenstowner Reece Gibson knows the rocky face of the Wakatipu’s intimidating Nevis Bluff like the back of his hand.
“Probably better,” the Opus geo-technical engineer says.
Gibson, 35, has regularly inspected the huge bluff, overhanging the State Highway between Queenstown and Cromwell, for 12 years – basically since graduating from university.
At one stage he even had a piece of it named after him – “Reece’s Rock” – but it only lasted two weeks before it was blown to smithereens by explosives.
It would’ve been blasted no doubt as a result of one of his monthly inspection reports to the Government’s New Zealand Transport Agency (NZTA). NZTA contracts Opus to monitor the Nevis and ensure it’s as safe as possible for drivers passing underneath.
NZTA has a budget of $200,000 a year for the Nevis, part of which gets spent on Opus’ monthly inspections by helicopter with Gibson on board.
On a recent trip – in which Mountain Scene was invited to tag along – Gibson is joined by fellow geo-technical engineers Rob and Lisa Bond, who tells me she goes up every few months as another set of eyes.
Heliworks pilot Jason Laing has been flying inspection trips for more than a decade and, like Gibson, is pretty familiar with the rock face.
Laing gets the chopper within five metres of it at times so the engineers can take a close-up look.
“As soon as we stop and start talking about a piece of rock, I try to show them from three or four different angles,” Laing says.
At one point, Laing zeroes in on a particular feature, saying it always looks a bit loose to him.
Gibson says: “Yeah, the abseilers have had a good go at that with the bars and couldn’t move it.”
The engineers use the trips to make note of anything that might be loose or features which are changing – and identify areas that might need blasting with explosives.
Post-inspection work can involve anything from abseilers brushing off debris by hand or using bars to dislodge rocks – plus drilling holes and inserting explosives. At times, heavy-duty bolts are used to strengthen certain sections.
“The heli-inspection is critical,” Rob says. “It’s the only way you’re seeing the whole bluff.
“We’ve compared it to other significant bluffs around the world and their experts all come back and say the best method is regular inspection. We’re incredibly lucky to be able to inspect by helicopter every month.”
An important part of the inspection process involves traffic management. Vehicles are prevented from driving underneath while the chopper flies close to the face as the whirring of the rotor blades has been known to dislodge loose debris. Similarly, on-ground staff try to keep kayakers out of the associated stretch of the Kawarau River.
The chopper buzzes away from the face every 10 minutes to let the built-up traffic through.
All up, they spend about 90 minutes in the air scanning the face which is about 800 metres long and 150 metres high. The sheer scale of it is breathtaking from the air and not apparent when driving underneath.
Lisa remarks: “Once you actually see it like this it makes you want to drive through as quick as you can.”
In reality, Gibson feels its risks are well managed, but doesn’t rule out another major collapse similar to the near-catastrophe of 2001.
“There’s the potential for that to happen. But we have a reasonable handle now on its failure mechanism.”
Back then, the Government had only just reintroduced monitoring after little had happened since a 1983 slip.
NZTA Central Otago area manager John Jarvis says back in 2001 he’d not long arrived on the scene and was concerned not much was being done.
“We’d actually started looking at the bluff, not on a monthly basis but had done a recent inspection and did identify the feature that failed.
“It looked like it posed a bit of a risk and it turned out that it did. We hadn’t sorted out what we were going to do with it. It demonstrated how quickly things can deteriorate up there and that we need to act as quickly as possible to mitigate the risks.”
Jarvis says the monthly checks are vital: “Doing this proactive work is certainly a step up on what we were doing, say, 15 years ago.”