Work on gorge’s large slip begins
Work has finally begun to clear the large slip blocking the Manawatu Gorge, four days after it came down.
State Highway 3 through the gorge is set to be shut for three weeks after two slips blocked both lanes of the main link between Manawatu and the eastern regions of the North Island.
The smaller of the two slips has been cleared and work began on the larger slip at the Woodville end of the road on Thursday, afternoon after geotechnical engineers finished their assessment of the area.
The road is expected to reopen on May 18.
NZ Transport Agency highway manager Ross I’anson said he was confident the slip was caused by heavy rainfall in the area over the past month.
Further rock fall netting would help minimise slips, but NZTA would also look at other options in the future, he said.
Horizons Regional Council chairman Bruce Gordon said he was disappointed that efforts to clear the slip had not been made sooner.
‘‘They don’t need to be sucking eggs. The people that have been working on the gorge are experienced with it.’’
In 2011, a large slip closed the Manawatu Gorge road for 14 months and two slips in 2015 also blocked the road.
Nothing could be done to prevent slips in the gorge, so an alternative route was the only viable option long-term, Gordon said.
Driving through the gorge was like playing Russian roulette.
‘‘What we’ve been told about the geology is that the rock formations are unstable.’’
An alternative to the gorge road, such as a tunnel or viaduct, needed to be put in the Government’s long term plan instead of constantly ‘‘patch-working’’, Gordon said.
The viaduct on the State Highway running through Otira Gorge near Arthur’s Pass in the South Island had proven successful and it would be the best solution for the gorge, he said.
‘‘It can’t just be left to carry on. It’s costing millions of dollars.’’
The slip in 2011 cost $15.8 million to repair and in 2015, more than $800,000 was spent on two major slips.
Massey University environment associate professor Ian Fuller said Manawatu experienced twice its average monthly rainfall in April, so slips were no surprise.
‘‘Heavy or prolonged rain is the most common cause of slips in the gorge.
‘‘We live in a country with lots of steep slopes, so slips are a fact of life.’’
Slopes where native forest had been cleared would always be more vulnerable to slips because trees helped dry the slope by intercepting rainfall and taking water from the soil, Fuller said.
Good canopy cover with vegetation and plantation forest could help minimise slips.
‘‘The problem in the gorge is the scale of some of these slips. When large portions of the slope slide, nothing can be done to prevent them from falling onto the road in its current alignment.’’
An alternative route is Saddle Rd, where a $8.4m upgrade has been halted while the gorge is closed to allow for the heavier traffic flow.
The Saddle Rd route takes about double the time of the gorge route.
Tararua Alliance spokesman Ray Cannon said the upgrade was delayed by one year due to wet weather and was expected to be complete by April 2018.
Saddle Rd was briefly blocked on Thursday when a truck caught fire. The driver suffered minor injuries.