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SH4 slip banner photo credit Mark Brimblecombe Photography

Project introduction

Ongoing works to repair storm, flooding and slip damage on State Highway 4 between Whanganui and Raetihi.

Reinstatement solution announced

Find out more about the reinstatement solution

The public are advised to stay up-to-date via the Journey planner website or 0800 4 HIGHWAYS (0800 44 44 49). Signage at the Raetihi and Whanganui entrances to SH4 will also be updated as conditions change.

For regular updates as repair works progresses visit www.journeys.nzta.govt.nz/manawatu-whanganui/roadwork-updates

If you use SH4 and were affected by the October 2019 slip, we’d appreciate your feedback to our emergency response by answering this short survey.

Start the survey

  • Estimated project dates

    Jun 2015–Jun 2020
  • Project type

    Road maintenance
  • Project status

    Maintenance

Project updates

State Highway 4 update
Newsletter,
State Highway 4 update
Newsletter,
State Highway 4 update
Newsletter,
State Highway 4 update
Newsletter,
State Highway 4 update
Newsletter,

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Background

In June 2015 a major flood event in and around Whanganui caused substantial damage to parts of SH4 between Whanganui and Raetihi. SH4 Anzac Parade in Whanganui and SH54 between Cheltenham to Vinegar Hill were also affected. The storm left a lot of silt and debris on the road, slips covering the road and drop outs where the road has fallen away. Work to repair this substantial damage, including repairs to the riverbank along Anzac Parade in Whanganui, is ongoing.

On 2 October 2019 a major slip on SH4 south of Raetihi destroyed a large section of the road, forcing it to be closed. This is unrelated to any of the previous resilience works on SH4.

Stay up to date

Frequently asked questions – SH4 slip

  • Is the temporary road on SH4 open?

    The temporary road is now open to all traffic including heavy vehicles. The health and safety of the public is paramount so the site will be constantly monitored, and if there are ever any safety concerns, it could be closed immediately.

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  • Why was SH4 closed south of Raetihi in 2019?

    An underslip on 28-29 September created a tension crack, resulting in two separate slip locations approximately 200m apart. SH4 remained open and the site was actively monitored. On 2 October, NZTA closed the state highway, due to the deterioration in the condition of the road, and the development of a significant slip circle above the road.

    A new temporary road through this section opened on 20 December 2019. The road is open to all traffic.

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  • Were there any indications this land would slip?

    SH4 has experienced damage from severe weather events over the years, mainly the 2015 floods, which we’re working to fix. But this slip hadn’t been mapped as an area of concern. It doesn’t show on the national landslide database from geology experts GNS Science, so there was no way of predetermining that the slip was going to occur. This is the case for many areas along SH4, which are prone to ongoing weather events.

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  • Is the site still moving?

    The slip site has stopped moving, except for in one location, which is why we're able to construct the temporary road. The area that is still moving is being closely monitored and is not presenting a risk to motorists at present.

    There were also some cracks that appeared over the Christmas period. These cracks were checked, are being continually monitored and haven’t shown any change.

    The site will continue to be monitored 24/7. If further slipping occurs, the road could be shut at short notice. Work to reinstate the road after any future closures will happen quickly.

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  • Are there other sites on SH4 that could slip as well?

    This site was not flagged in the initial surveying of the region by geology experts GNS Science. It’s possible there are other similar sites. This is true of many roads around the country that use a river course to plot a path through the surrounding landscape.

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