Nevis Bluff delays having ‘severe impact’
Roadworks signage for blasting and drilling at the Nevis Bluff may be erected at Cromwell and at the base of the Crown Range road, so motorists get the information in time to take an alternative route. Central Otago District mayor Tony Lepper said last month the frequent delays at the bluff were frustrating motorists and stifling the economy. ‘‘I’m noticing lots and lots of vehicles, lots of people changing their schedule. I’m adding an hour to my journey, just to go to Queenstown. My time is precious. Everyone else’s is just as precious. ‘‘If you count every car there and add up the hourly rate, I think [the impact on the economy] is severe.’’ Traffic is delayed for 20 minutes during monthly assessments of the bluff and for an hour if blasting is needed. Vehicles are also stopped every time a helicopter is used to drop equipment off onto the bluff. Mr Lepper asked the New Zealand Transport Agency to produce its long-term plan for dealing with the risks created by the bluff, saying motorists’ frustrations may ease if they better understood the problem and when – or if – a permanent solution would be in place. The agency’s Central Otago area manager, John Jarvis, told the Mirror there was no permanent solution on the table and motorists who wished to use State Highway 6 between Queenstown and Cromwell simply had to accept delays due to the nature of the landscape. Construction of rock protection fences and bunds was being seriously considered, but these would only prevent small rocks from falling onto the road, he said. While this would make the highway significantly safer for motorists, it would not reduce disruption to traffic because the large unstable rocks – sometimes the size of utes – would still need to be blasted off using dynamite or bolted on. Project engineer Reece Gibson agreed motorists would be less frustrated if they understood the problem that the 800m long and 140m high bluff posed. ‘‘They can’t see what’s going on and, by the time they drive past, the guys have cleared the rocks off the road. Anyone we’ve brought up in a helicopter has gone ‘wow’. They didn’t realise it was like this. ‘‘In terms of geological challenges, there’s nothing quite like it anywhere else in the country.’’ The road, which opened in 1867, was covered by massive slips in 1975 and 2000, of 30,000 and 10,000 cubic metres of rocks respectively. No-one was killed in either of the slips, although a group of motorcyclists had a near miss in 2000 when rocks ranging in size from a car to a double garage tumbled onto the road. There are now two rockfalls a year on average, of up to a dozen fist-sized rocks, and no cars have been hit for seven years. Mr Jarvis said fences and bunds were the only feasible option at present and he hoped to trial at least one of them within five years. Several total solutions were considered – and disregarded – in 2001, including covering the road with a ‘‘rock shed,’’ building a bridge across the Kawarau River at both ends of the bluff, cantilevering part of the road over the river, building a suspension bridge or a viaduct, with piers in the riverbed, or realigning the road to go behind the bluff with a ramp down into the Gibbston Valley. ‘‘These are things the public thinks are the answer but, in this situation, it’s not as simple as that.’’ Two options which are considered to be more feasible – but are not on the radar – are terracing the bluff, called ‘‘earthwork benching,’’ so falling rocks are caught before they reach the road, or building a 650m long and 10m wide tunnel. But both options were far too costly at the moment.
Big task: The 800 metre long and 140m high Nevis Bluff— engineers working to stabilise it say there is nothing as geologically challenging on any other New Zealand road. Photo: JESSICA MADDOCK/
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Abseilers hang 170m above State Highway 6 this week, to drill seven to 12m long bolts into the Nevis Bluff to stabilise the rock.