State Highway 38 (SH38) was damaged by Cyclone Gabrielle in February 2023. The Transport Rebuild East Coast (TREC) Alliance is delivering recovery work to restore this road back to two lanes.
The TREC team has made steady progress repairing underslips on SH38, typical of the kind of damage left behind by Cyclone Gabrielle.
Underslips happen on the downhill side of the road and pose a risk to the road above if they aren’t addressed. Because most of the work is out of sight below the road, it can be difficult to see what’s happening when you're travelling by.
SH38 recovery map
TREC has made steady progress repairing the underslips typical of the kind of damage left behind by Cyclone Gabrielle. We have completed six recovery projects along the road, including the sites shown here.
Waikaretāheke River Underslips
Underslips occurred along the section of the road that runs next to the Waikaretāheke River. Two slips were repaired in early 2023 by NZTA and TREC completed the remaining two underslips in February and April 2024.
Waikaretāheke River Underslip 3 was completed in April 2024:
Waikaretāheke River Underslip 4 was completed in February 2024:
Piripaua Scour
This site, near the Piripaua Power Station, was completed in October 2024.
After the old slip material was removed, geofabric cloth (the white sheets in the photo) was installed against the cleared slope. Geofabric cloth prevents materials from mixing while allowing water to pass through it without washing the materials away.
The team then uses aggregate (a mixture of different types and sizes of crushed rocks) to build the bank back, stabilise the ground and restore the road to two lanes.
Waiau River Underslip
This site was completed in September 2024.
South of Mangakino Bridge Scour
This site was completed in October 2024.
There are six recovery projects currently in design. These are:
We expect to have the designs finalised this year.
To start the underslip repair, we first dig a track down to the bottom of the underslip so the team can access the site and remove the old slip material.
Once the material is gone, geofabric cloth is installed against the cleared slope. Geofabric cloth prevents materials from mixing while allowing water to pass through it without washing the materials away. We then use aggregate (a mixture of different types and sizes of crushed rocks) to build the bank back.
Another layer of the geofabric cloth is laid down to keep the aggregate in place. Rock armour is placed on top of the geofabric to protect the aggregates from being washed away by flooding. This repair method helps stabilise the ground under the road and protect the bank from future erosion.
The reinstated bank is then hydroseeded. Hydroseeding is when we spray a slurry of seeds, mulch, and fertiliser onto steep slopes to provide stability as well as helping to control dust, erosion, and sediment runoff.
The Nature’s Road project aims to improve the safety and resilience of SH38/Special Purpose Road between Wairoa and Murupara for local communities, Ngāi Tūhoe, and visitors.
The project will see an environmentally sustainable material used to treat the road to respect and care for nature in Te Urewera. Safety improvements are also being made to the route.
A key component of the project is working in true partnership with Ngāi Tūhoe iwi, recognising that each party brings valuable expertise, skills, values and ways of working.
As you can see on the map, some of our recovery work is within Nature’s Road section three. We are working with Ngāi Tūhoe iwi to make sure we are using the appropriate designs, materials and methods for our recovery work on SH38.
