Plans for a cyclone-damaged stretch of State Highway 35 at Mangahauini Gorge are being developed, with work focused on stabilising the hillside and protecting the road from the energy of the Mangahauini River.

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

SH35 Mangahauini Gorge is an important connection for the East Coast and has 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.

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 said work at Mangahauini Gorge has been underway since Cyclone Gabrielle but there’s more to be done.

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

“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,” said Bayley.

“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,” he said.

“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.