Manawatu Gorge: Simon Bridges hints at big bucks alternative

by Pattrick Smellie / 27 July, 2017
RelatedArticlesModule - Manawatu Gorge

Slips have blocked the Manawatu Gorge route half a dozen times since 1990. Photo/One Shot

When is a road of national significance not a Road of National Significance? Answer: when it’s the Manawatu Gorge.

Except, of course, that the closed road link between the east and west of the lower North Island is so clearly a road “with” national significance that the Government is going to have to replace it.

The usually cautious Transport Minister, Simon Bridges, readily concedes that just doing up a couple of temporary, hilly back routes won’t cut it. “We’ve reopened this road four times. Every time the slips are cleared and repaired, more happen. At the moment, the gorge has been out for 340 days and counting in the past decade.”

In other words, the important link between the Manawatu and Hawke’s Bay regions is now closed one day in 10. “That’s just not good enough,” says Bridges.

With Palmerston North increasingly operating as a freight hub, the damage to Wellington’s port from last November’s Kaikoura earthquake has seen a surge in freight through the gorge from Manawatu and Whanganui to the Port of Napier.

The trouble is that the replacement options are neither cheap nor easy.

Cut by Maori and European settlers on the southern side of the steep-sided Manawatu River gorge, the route opened as a narrow track in 1872. Progressive widenings throughout the 20th century saw the road hewn deeper into cliff faces that GNS Science, the Government’s geologist, says have been sliding into the river for at least half a million years.

Major slips have closed the gorge in 1990, 1994, 1998, 2004, 2011 – when it was off-limits for a year – 2014 and May this year. And just as yet another clearance operation was getting into full swing, geologists checking for land movement recorded a sudden acceleration.

“The pace of movement is significantly increasing,” says Bridges. A 60mm movement in the previous 18 months became an 80mm movement in one month.

Until that’s understood, it’s no longer safe to work in the gorge and it is now closed indefinitely. Years of avoiding the question of an alternative road appear to be over.

Simon Bridges. Photo/David White

“We definitely need a new route,” says Palmerston North MP, Labour’s Iain Lees-Galloway. His pick is major investment in Saddle Rd, the windy, hilly route to the north, which already carries most of the traffic that would otherwise use the gorge.

Some $8.5 million of short-term upgrades are under way already and add to the cost of work after the 2011 slip, and more are being urgently planned now, since a permanent replacement route will take anywhere from seven and 10 years to complete.

To the south, the so-called Pahiatua Track route is also carrying extra traffic. Whereas Woodville and nearby towns are reporting a slump in business, others further south in the Wairarapa are seeing more traffic than usual coming through from Wellington.

However, the traffic volumes involved are small by national standards – about 7500 vehicles a day. The Auckland Harbour Bridge carried more than 11,000 vehicles the day it opened in 1959 and as many as 200,000 a day cross it now.

As a result, says Bridges, normal cost-benefit calculations on replacement options for the gorge road are “pretty ugly”. On the other hand, about 18% of that traffic is heavy freight vehicles, a high proportion by national standards.

Saddle Rd, which could be replaced for $120 million as a substitute for the gorge road. Photo/Alamy

Saddle Rd, which could be replaced for $120 million as a substitute for the gorge road. Photo/Alamy

Ways to go

A 2012 study by the New Zealand Transport Agency (NZTA) identified four potential alternatives, including one that would upgrade the route using bridges and tunnels to take the road away from the gorge edge. That would cost an estimated $415 million and appears to be the least-favoured option since parts of the road would remain vulnerable to slips.

A second option is to put a road straight through the hills to the south of the gorge at an estimated cost of $309 million, although it would also be slip-prone because it would require deep cuts to create a route that was flat and fast enough.

A tunnel beneath the northern end of the Tararua Ranges has also been considered, at a ballpark cost of $1.8 billion, but comes with the warning that anything could happen if the project struck unexpected geological challenges in a tunnel nearly twice the length of Auckland’s new Waterview connection.

Iain Lees-Galloway foresees a different solution. Photo/Getty Images

Which leaves the least-exciting and longest option – a new 10.6km road to replace Saddle Rd for an estimated $120 million. Whereas Lees-Galloway thinks that’s the logical answer, Bridges seems resigned to a costlier outcome.

“There should be no false hope about what may come out of that, because the options in 2012 ranged from $180 million to $1.8 billion,” Bridges told the Listener. “The more likely solution will be to do something very different to what’s there now and at the higher end rather than the lower.

“That’s the more likely scenario. It could be in the gorge. It would have to be more than just clearing and repairing.”

Whereas the NZTA concluded in 2012 that a replacement route was “not justified”, Bridges is suggesting that if the gorge sides keep moving and the route can’t be reopened, a new route is inevitable.

“The overriding social and economic effect would be significant” if the gorge was left closed, even though “when you match that against an $800 million road … the conventional transport logic isn’t there”.

Pahiatua Track, which is taking some of the gorge traffic. Photo/One Shot

Pahiatua Track, which is taking some of the gorge traffic. Photo/One Shot

“But what price do you put on those who use it and need it? There are some roads where you have to have them.”

Road Transport Forum executive director Ken Shirley, who represents truckies, says the link is “vital” and is dismissive of any suggestion of the rail link on the other side of the gorge being a big part of the solution. But KiwiRail chief executive Peter Reidy says not so fast.

The rail line on the northern side of the river is occasionally closed by slips – the worst recently was for three days – but that side of the gorge drains better and much of the line is protected by existing tunnels. “It’s a corridor with plenty of density and capacity. We would be only too happy to add resilience to road,” says Reidy, who faces the challenge of justifying a business that simply cannot be profitable because the cost of the rail network outweighs the freight volumes available to it.

Anything that can prove the wider worth of rail to the nation is music to his ears. “It’s good for the Government to be able to say: ‘The road may be out, but rail’s there.’”

This article was first published in the July 29, 2017 issue of the New Zealand Listener.


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