SH4 Whanganui to Raetihi repairs

24 August 2023

The newly constructed section of road on SH4 south of Raetihi

Road retreat nearly complete!

The Auraki Stream Road Retreat project south of Raetihi is now nearing completion.

In previous updates we've reported on the big job it's been to relocate 400m of the road away from where it was affected by a slip beside the Mangawhero River. This work has been underway since December 2021.

The project has involved retreating (or cutting back) a hill over 55m in height, extension and addition of culverts, pine tree felling, temporary stream diversions, rock bolting/mesh work to stabilise ground, and more. Due to a separate underslip close by, construction of a new gabion wall and rip rap (rock) revetment (retaining wall) extending from the Mangawhero River up to the gabion wall was also added to the project.

In June, we were able to move traffic onto the southbound lane of the new section of road. Then last month, we opened the road to two lanes during nights.

The next step in the coming weeks is undertaking chip sealing, followed by line marking, when the weather is fine. Some other final works include guardrail installation, fencing, drainage work, planting and completing a small new wetland area away from the road.

As well as Horizons Regional Council, both Whanganui District Council and Ruapehu District Council have been involved in this project as it straddles the boundary of the two councils.

Auraki Stream running over new rock riprap - a route for fish

A focus on fish passage

We posted on Facebook recently about the special care taken to ensure fish could continue to easily pass through Auraki Stream, given we needed to install a 25m long culvert extension in the stream as part of the project.

This has been a real highlight of the project. We used rock to recreate natural stream beds and create eddies and small pools inside additional new and existing culverts for fish to pass through and rest in. Also, to ensure that Auraki Stream wasn't simply lost into the depths of the rock rip rap revetment works, we filled the voids between the rock with concrete—enabling the awa to pass over land and further enhancing fish passage. 

Planting day a positive milestone

On Friday 18 August, a community planting day was held at the Auraki Stream road retreat project site.

Children from local schools joined with representatives of Waka Kotahi, Beca, Higgins and Mills Albert, and project partners Ngāti Rangi, Uenuku and Te Korowai o te Awaiti for the day.

Aberfeldy School, Kakatahi School and Te Kura Kaupapa Māori o Ngāti Rangi helped with the planting and were able to check out some of the machinery on site.

See what Kakatahi School had to say about the day in this Facebook post!

Around 11,000 plants will be planted in the area as part of the project. They will help to mitigate the effects of the project works and hopefully attract kererū back into the area.

Works have started on new retaining walls at the Te Oreore slip site

Works at Te Oreore slip site

Since March this year we've been undertaking some important works at the Te Oreore slip site to ensure the ongoing safety and reslience of the route.

This is the site of a major slip in 2019, where there is a temporary road in place.

The work underway now includes the construction of three new retaining walls north of the main slip area, and the drilling and construction of two new dewatering wells. This work is needed as a result of heavy rain last winter which caused some ground movement at the slip site. This work will prevent further movement and safeguard the area so we can keep working towards the permanent road replacement.

We are still working through the planning required for the permanent road project (read on for more detail on this below) and will keep stakeholders and community updated of future milestones. In the meantime, ongoing dewatering and monitoring is in place, along with a 30km/h speed limit. If you are a regular user of SH4, thank you for your patience here.

Iwi, hapū and Waka Kotahi representatives together at Tuhiariki Marae earlier this year

Hapū voice at centre of project

An ongoing focus ahead of construction of the new permanent road at the Te Oreore slip site is working with mana whenua to ensure any plans support the objectives of Te Waiū-o-Te-Ika Framework for the Whangaehu River catchment.

This year, a series of focused iwi and hapū wānanga have been held to work through the plans that Waka Kotahi has for the reinstatement of the road.

Troy Brown, Ngāi Tuihariki, says, “hapū voice has been at the forefront of this project, and we will work hard to ensure this happens throughout the entire process”.

“A highlight is Ngāi Tuhiariki has had space to wānanga about what’s important for us and how we are going to protect our taonga.”

“We’ve been given the time we needed to work together as a hapū, ask the technical questions of Waka Kotahi, and then collectively speak to the interests of our whenua.”

Environmental and cultural experts have been resourced by the project, and local iwi, Ngāti Rangi, is supporting the process.

The project partners are now working together to agree how a range of important cultural and environmental considerations will be addressed. Co-design workshops to take this mahi forward are coming up. Following this, a key milestone will be applying for consents to begin construction in early 2024.

Waka Kotahi recognises and respects Te Tiriti o Waitangi (the Treaty of Waitangi) and will work with Māori as partners to build strong, meaningful and enduring relationships to achieve mutually beneficial outcomes.

Other works underway on SH4 Parapara Rd

SH4 Parapara Road has been significantly impacted by weather events in the last decade, including Gabrielle recently. As a result we continue to undertake work at multiple sites along the route.

During a two-day full closure in June this year, we did some initial works at the site of a washout north of Hawken Road (temporary culvert installation and shoulder widening). Work at this project site continues, with construction of a rock wall to repair the slip now underway.

During the closure in June we also undertook dangerous tree removal, inspections of bridges and other structures, general maintenance along the route, and motorcycle safety improvements.

'Culvert 45' is the name of another project underway currently on the route, near Burrell Road, to remediate multiple underslips and subsidence. This involves backfilling and consolidating slip areas, formation of benching, and culvert repair work.

Design is also underway currently for important resilience/repair works at a number of additional sites along the route, including some remaining Cyclone Gabrielle damage sites.

More information

For more information on the SH4 Whanganui to Raetihi repair projects, contact us at SH4@nzta.govt.nz

Visit our website www.nzta.govt.nz/sh4-repairs