New Manawatū Gorge route shouldn't go through slip-prone gully
An alternative route to the damaged highway through the Manawatū Gorge should avoid the troublesome gully completely – and the railway should be moved too, a senior geographer says.
The NZ Transport Agency has released 13 alternative-route options for the main highway between Hawke's Bay and Manawatū, as the old State Highway 3 through the gorge is closed indefinitely after unstable rock was discovered.
The transport agency predicts up to 630,000 cubic metres of further material could fall, which is 170 times more rockfall than the two slips that closed the road in April.
Three of the 13 options run through the gorge, which Massey University physical geography senior lecturer Sam McColl said should be avoided.
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The railway track through the gorge, on the Ruahine Range side, should also be moved, as it was prone to landslides, McColl said.
Although that would significantly increase costs in the short term, it would have long-term benefits, he said.
"If there was any cost efficiency to be gained from realigning road and rail at the same time this might be an option worth considering."
KiwiRail spokesman Todd Moyle said there had been 19 reported slips or debris on the rail line through the gorge in the past five years, but most of those were minor.
Only one slip led to the closure of the rail corridor, for about three hours, Moyle said.
"We have no plans to shift or close the line."
A major slip in 2010 closed the railway line for about a week. Before that, the last train through the gorge to hit a slip was in 1998.
In August 1946, engine driver Basil Craighead and fireman R Hoskins were killed when their 140-tonne steam engine hit a slip and crashed into the flooded Manawatū River.
Horizons Regional Council chairman Bruce Gordon said the gorge was still an good option as a viaduct similar to the one at Arthur's Pass in the South Island could work.
Gordon didn't say which option he preferred, but he said a flat route would be best.
"Whatever happens, it must take a 50-year view for the better of our region.
"I don't want to see a patch up."
Gordon was surprised at the number of options and said it should have been narrowed down before it went to public consultation.
Transport agency regional transport systems manager Ross I'Anson has said the public asked the transport agency to share the information as it was developed.
Palmerston North mayor Grant Smith said it was clear that some of the options would not get any traction.
"Let's be totally honest, the ones going through the middle of Ashhurst, they are scrubbed.
"There's a clear message from the community that they don't want them to go through Ashhurst."
The council would echo this to roading officials, Smith said.
"I don't even know why they are in the picture. They created quite a lot of angst."
The gorge was "riddled with issues" and a full-blown tunnel would cost billions.
The council would be pushing for a four-lane route that had a separate cycle lane, Smith said.
Manawatū mayor Helen Worboys said people were quick to criticise the transport agency.
"In this instance, I know they've dropped everything and fast-tracked it."
The 13 options will be narrowed down by the time open days are held at the Palmerston North Conference and Function Centre and the Woodville Sports Stadium on October 11 and 12.