Waka Kotahi is warning of the potential for SH1 through the Mangamuka Gorge to remain closed for some time, following significant damage caused to the highway from torrential rain this month.

Waka Kotahi regional transport systems manager Jacqui Hori-Hoult says a timeline for rebuilding and re-opening the highway through the gorge won’t be known until geotechnical engineers have carried out detailed assessments of all of the damage sites.

“Our crews have only been able to gain safe access to some areas in the past day, with conditions in the gorge still highly unstable. Even with the fine weather currently, parts of the road and surrounding hillsides are continuing to move.

“We’re dealing with more than a half dozen major slips and underslips following this rain event. The soil in this area is generally soft and unstable to begin with, which makes the stability of the land in the gorge particularly susceptible to the effects of severe weather, including more frequent and heavier rain storm events and conversely drought conditions in summer.”

The most recent heavy rain has caused five new underslips in the gorge (with movement of land below the road). Three of these underslips are currently being investigated by geotechnical specialists to determine the most effective permanent solutions for stabilisng the land. The remaining two underslips have been identified as ‘slow movement sites’, which will continue to be monitored to determine the rate of movement and the potential need for longer term remedial works.

“We closely monitor all known land movement and slips in the Mangamuka Gorge, as we do for all state highways, but the increasing frequency and intensity of severe weather events as a result of climate change means that slips and closures are becoming more common, on state highways as well as on local roads.

“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.”

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

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