Initial assessment of SH4 highlights scale of the slip


15 October 2019

Initial findings from the geotechnical investigation into the large hillside slip that caused significant damage to State Highway 4 confirm that the work to reinstate the route will be significant and complex.

Following a meeting with geotechnical engineers investigating the slip, NZ Transport Agency Journey Optimisation Manager Lance Kennedy says more work needs to be done to fully understand the type of repairs required and the approximate timeframe for reinstating the road.

“The site is still highly unstable and remains fully closed off. It is continuing to move and any rain in the next few weeks is likely to exacerbate the slip movement.

“Given no one can access the site until it stops moving, geotechnical engineers have been assessing the site remotely using drones. These initial assessments have painted a clearer picture of the scale and complexity of the slip.

“At its widest point the slip is approximately 400 metres wide. It is around 200 metres high and could be up to 50 metres deep. Estimates are that there is around 30 hectares of material that could slip, of which around 15 to 20 hectares has already moved.


"To put this into context, the size of this slip is similar to the large slips in the Manawatu Gorge in 2011.

"There is still a lot more work to do to understand how the site is going to change over time. We will continue to monitor the site remotely until it is stable enough for ground crews to enter safely. The safety of road users and workers is paramount.

“We know how important this road is to road users, businesses and locals. Finding a safe solution for reinstating the road is a high priority, but given the scale and complexity of this slip it is going to take some time and a considerable effort,” Mr Kennedy says.

The road will likely remain closed for a significant time and road users are advised to plan ahead.

The Transport Agency reminds road users that the recommended detour route is via State Highway 1 and State Highway 49, which will add at least one hour to the journey.


Photos show the scale of the slip on SH4. Photos courtesy of Mark Brimblecombe.




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