State highways south of Napier were damaged during Cyclone Gabrielle in February 2023. The Transport Rebuild East Coast (TREC) Alliance is delivering recovery work to restore these highways back to two lanes.
The damage from Cyclone Gabrielle on SH50 affected five bridges, one culvert and created a significant underslip near Maraekākao.
On SH51, the Tutaekuri bridge on SH51 was damaged.
On SH2 south of Napier there were two culverts that needed substantial debris clearance in order to continue to work effectively.
Repairs and strengthening work on the Ben Lomond Bridge between Maraekākaho and Tikokino were completed in October 2024.
The bridge, built in 1973 across the Maraekākaho river, had intense flows during Cyclone Gabrielle. These flows and additional storms wore away the riverbanks opposite the northern pier, potentially weakening the ends of the bridge where it rejoins the hillside and the structural integrity of the bridge.
To prevent erosion we installed geofabric along with 400 tonnes of riprap (large rocks) on top of this. These large riprap rocks placed along the edge act as a shield. They absorb the force of the water, protecting the soil and keeping the riverbank intact, resulting in protection to the bridge’s foundations.
Recovery works at Glencoe Gorge were completed in October 2024. The site is five minutes south of Maraekākaho, where heavy rain caused significant damage to the Glencoe Culvert and retaining wall.
The damage caused water to enter the culvert’s foundation, increasing the potential for erosion. The damaged culvert was repaired and strengthened by raising it to the road level. This will improve drainage and better manage water surface runoff.
The existing retaining wall had buckled over due to the tension from heavy rain causing cracks. Crews excavated the roadside to remove and replace the existing walls and then rebuilt the road above.
During Cyclone Gabrielle, floodwaters scoured (eroded) away part of the bank underneath Mangamate Stream Bridge, compromising the bridge abutment which connects it to the land.
The road shoulder slumped away, and the road was down to a single lane. The bridge abutment was reasonably challenging to repair during the winter with water levels going up and down.
Repairs were focused around increasing ground stability to provide resilience for the road whenever the ground becomes waterlogged. Specialist crews installed 26 ground anchors to stabilise the bank and support the bridge and road above. The team drilled holes up to 12m deep, placing the steel anchors into the holes and grouting them into place. Ground anchors are long steel rods which give the ground and road extra stability. They are a crucial part of the recovery work.
The road reopened to two lanes in October 2024.
Glencoe Gorge Underslip
The final recovery project on SH50 will begin in early 2025.
The Glencoe Gorge underslip is around 15m high and 10m wide and has undermined the existing guardrail and farm fence located along SH50.
When there is an underslip on the downhill side of the road it poses a risk to the road above if it isn’t addressed. Because underslips are usually out of sight below the road, it can be difficult to see the damage and what’s happening to fix it when you’re travelling past.
To start the repair, we’ll first dig a track down to the bottom of the underslip so the team can access the site and remove the old slip material. There will also be a temporary stream diversion to protect aquatic life. An EcoReef wall, made from hexagonal blocks filled with material will be constructed to protect against future erosion. The edge of the road surface is then reinstated and new guardrail is installed.
This job, and our work on SH50 is expected to be complete by autumn 2025.
SH51 Waitangi Bridge (Tutaekuri River)
Recovery work at this site is in design with programmed construction start expected in May 2025.
Recovery work could include repairing the damaged piles above the waterline and replacing the damaged cycleway bracing. Debris will also need to be cleared away from the bridge with road settlement monitoring sensors installed.
Most of the Cyclone Gabrielle damage on SH2 occurred north of Napier but there were two damaged culverts in the south - Okahupupuni Stream Culvert and Awanui Culvert.
TREC had to clear substantial debris from these culverts to help channel water with the aim of protecting the road above them and the land supporting the road from excessive water damage.
These sites were cleared in early 2024.
