Work progressing to assess SH1 damage through Mangamuka Gorge


Work is progressing to assess the full extent of damage sustained on SH1 through the Mangamuka Gorge following this month’s torrential rainfall.

Waka Kotahi contractors have worked to cut a temporary track through the largest slip covering the road at the southern end of the gorge to allow access for construction vehicles to pass through, and crews are now working to clearing slips further south.

A temporary track has been cut through this large slip at the southern end of the gorge.

Waka Kotahi Auckland/Northland Regional Manager Jacqui Hori-Hoult says a geotechnical engineer and a specialist drill machine operator are also on site to perform the geotechnical assessments required to understand the extent of the damage.

“The drill rig being used for this work weighs roughly 10 tonnes, and it was necessary to ensure that the ground conditions could support bringing such a large piece of equipment through the slip site before moving the machinery in.

“Conditions in many parts of the gorge remain highly unstable, and the ground is still moving.  A further slip has developed under the road, bringing the total number of underslips to 15, in addition to the three overslips which crews are now working to clear.

“Under the direction of the specialist geotechnical engineer, crews are working to prevent any further damage to the current underslips, with bunds constructed to divert any further rainfall away from the slips.”

Ms Hori-Hoult says a timeline for rebuilding and re-opening the highway through the gorge won’t be known until detailed geotechnical assessments of all of the damage sites have been completed.

“We understand the importance of this route to the people of Northland, and we will provide an update on the extent of the damage and the likely timeline for completing repairs as soon as our damage assessments are complete.”

Ms Hori-Hoult says while Waka Kotahi closely monitors all known land movement and slips in the Mangamuka Gorge the increasing frequency and intensity of severe weather events as a result of climate change means that slips and closures are becoming more common across New Zealand, on state highways as well as on local roads.

The detour route while SH1 through the gorge is closed is SH 10 via Kerikeri, Kaeo to Aawanui and to SH1 Kaitaia.

In order to ensure the continued movement of vital goods through the region, Waka Kotahi has also reinstated temporary access for over dimension vehicles to use the SH10 Waitangi River Bridge while SH1 remains closed through the Mangamuka Gorge.

Restrictions on use of the bridge were put in place earlier this year, following the detection of deterioration during a routine inspection.

The condition of the bridge is being very closely monitored, with a structural engineer checking the bridge daily. 

Photos of the damage sustained on SH1 through the Mangamuka Gorge are available