Rain-soaked slips on the move in Mangamuka Gorge on SH1


Assessment and clearance of slips on State Highway 1 through the Mangamuka Gorge has stopped at the top of the summit because there’s still movement on the hillside after last week’s deluge of rain.

Large crack in the road with road cones around.

The slip under the road is still moving and the road surface has dropped further since the weekend.

Metservice is forecasting some showers today, but the outlook is for the weather to improve by the weekend.

Friday’s deluge left eight significant slips and many smaller ones along a 12 km stretch of SH1 in the Mangamuka Gorge. Another slip appears to be forming south of the summit and the three biggest slips on the northern side are still moving, says Waka Kotahi NZ Transport Agency Northland System Manager Jacqui Hori-Hoult.

Road clearing crews have moved their equipment down the road away from the summit for now.

“There’s a huge safety issue for our workers at the moment and we’ll just have to wait rather than compromise on that.”

“We’ll also be putting up a drone so we get a view of what we can’t see from the road. There may be other slips and instability above the road in places and we need to take that into account.”

“The major overslip closing the road starts well up the hillside and there are big trees left hanging where the ground has fallen away. With expected rain and high winds this could loosen up more material to fall on to the road”

It’s not just the slips above the road that are still moving. Half the width of the road has slumped in one place and when compared to photos taken at the weekend, it has dropped further in the last couple of days.

On the southern side of the gorge, the slips are smaller and road crews have been working to clear them.

Ms Hori-Hoult says it may be possible to open the gorge to light vehicles, with the road in places reduced to one lane.

“We’ll know more on that next week. The team is working hard to ensure it is safe to open the road.”

For now, SH1 is closed between Victoria Valley Road and Makene Road. SH10 is the detour with motorists advised to allow an extra 20-30 minutes for their journey.

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