Ne­vis Bluff delays hav­ing ‘se­vere im­pact’

Central Otago Mirror - - FEATURES - By JESSICA MAD­DOCK

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/

FAIR­FAX NZ 627915555

Photo: JESSICA MAD­DOCK/FAIR­FAX NZ 627915552

Ab­seil­ers hang 170m above State High­way 6 this week, to drill seven to 12m long bolts into the Ne­vis Bluff to sta­bilise the rock.

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