More work set for Mangahauini Gorge

NZ Transport WakaKotahi is developing plans to further stabilise a section of the cyclone-damaged stretch of State Highway 35 at Mangahauini Gorge.

Further plans for a cyclone-damaged stretch of State Highway 35 (SH35) at Mangahauini Gorge have been under development.

The additional work focuses on stabilising the hillside and protecting the road from the energy of the Mangahauini River.

Transport Rebuild East Coast (TREC) alliance, on behalf of NZ Transport Agency Waka Kotahi (NZTA), will deliver the work alongside local contractors.

Construction will start on site once additional concept designs for the recovery work are finalised and resource consents are approved.

The aim is to begin this final phase of recovery work in the 2025/26 construction season.

Project manager Richard Bayley says work at Mangahauini Gorge has been under way since Cyclone Gabrielle but there’s more to be done.

“Since the cyclone, the focus has been on installing things like rock rip rap to provide road protection from the river, rebuilding lanes at drop-out sites and emergency works at the site of the landslide.

“The additional recovery work in the gorge is looking at further slope stabilisation and protection, river and road edge scour repairs, culvert and drainage upgrades, and road surface repairs and replacement.

“Dealing with landslide material, upgrading undersized culverts and drains and providing long-term solutions to the damaged sheet pile wall and embankment will be a key part of the additional recovery work, along with re-sealing the road. We will also investigate options for better protecting the highway from the force of the Mangahauini River. Design work for this starts this month.

“We’ll be looking at addressing issues left over from a landslide at the southern end of the gorge and helping to restore some resilience to the highway through the recovery construction process. For example, extending rock-armouring (protecting the river embankment with large rock walls) to help prevent the river from scouring out the foundation of the highway.

“Work to replace further sections of highway in the area and embankment lost to slips is expected to start in the coming 2024/25 construction season, subject to property access being granted.”

Bayley said SH35 Mangahauini Gorge was an important connection for the East Coast and had been allocated recovery funding from within the additional $250 million of funding allocated in Budget 2024 to recovery projects on cyclone-damaged East Coast highways.

“We are continuing to work closely with iwi/hapū partners, council, landowners and local contractors to design and deliver the highway recovery work in the gorge.

“The feedback we’ve received this year from communities is helping to shape our recovery work and influence the ongoing design planning.”