Manawatu Gorge Landslide Remediation

Restoring a vital transport link for communities on the east and west of the central North Island.

New Zealand Transport Agency  |  Manawatu, New Zealand



The Manawatu Gorge section of State Highway 3 is one of the most difficult roads in New Zealand to work on. This narrow road is carved into the side of the gorge 20 metres above a river. The road is a vital transport link for communities on the east and west of the central North Island.

Project Scope

MWH Global was the New Zealand Transport Agency’s (NZTA) network consultant and geotechnical engineer for the project. Together with a team of specialist geologists, geotechnical engineers, client manager and contractor.  MWH worked collaboratively, and with urgency, to reopen the highway.

MWH was responsible for:

  • management of the project to reinstate the highway and make the route safe
  • geotechnical analysis to identify the safest option for remediation of the landslide scar
  • creating the geological and excavation models to define a safe slope profile and monitor the clearance work as it was undertaken
  • modelling and risk analysis
  • design of the mesh drape and development of the rock fall attenuator fence
  • road alignment design.
Manawatu Gorge Remediation

(m) wide landslide

(m) Crest above road

Estimated cubic metres of loose rock and soil

Roading New Zealand Award

Project Challenge

Measuring 140 metres wide and with a crest 130 metres above the road, this is the largest road landslide in New Zealand’s history. The work carried out to stabilise and remediate the Manawatu Gorge slip has been a huge undertaking by all parties involved. While the initial slip was considered large, the on-going regression and final remedial design was far bigger than anyone initially comprehended.

Manawatu Gorge Remediation

Project Solution / Result

A collaborative team approach resulted in an expedient response and the safe removal of the slip material from the site by the end of May 2012. Initially thought to be a 26 month project the the road was opened to two-way traffic on 19 September 2012 13 months after the event and in under half the estimated time. Restoring a vital transportation link for the central North Island.

“The crew have stuck at the task for a long time, and they can now reflect on a job well done. They’ve rebuilt an entirely new piece of highway in a superbly orchestrated blur of activity, and words can’t express the value of their hard work for the Manawatu region and beyond. Every cliché about true grit and Kiwi ‘number eight wire’ ingenuity comes to mind, but at the end of the day, they had a job to do – a huge job – and they did it.”

David McGonigal

State Highways Regional Manager, New Zealand Transportation Agency

Manawatu Gorge Remediation

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