Why is SH35 vulnerable?
State Highway 35 (SH35) is built on challenging geological terrain. Highly erodible soils on top of weak geology make the road vulnerable, especially during weather events. Closures and disruptions have serious impacts to people, whānau and businesses, as it’s a critical link to the East Coast.
What is a resilient road?
Resilience is about maintaining access to communities, whānau and businesses. A resilient road can remain open and function during unforeseen events, as well as day-to-day use, and ideally has alternative routes. We want our roads to be able to withstand disruptive events.
A resilient road can perform effectively and adapt to changing conditions (including climate change) and recover quickly from disturbances.
What are the main challenges the state highway faces?
The geology of the East Coast is challenging. The rock is soft, unstable and full of water which affects the stability of the road.
The geology on this 335km coastal route is unstable and highly erodible. It’s estimated that 26% of the region’s land is susceptible to severe soil erosion, compared with only 8% of all land in New Zealand.
The slopes can’t always be stabilised with engineering only. We need to engineer solutions that work with the enviornment to ensure the most robust roads possible.
What is being done to improve the resilience of SH35?
The Tairāwhiti Roading Package, funded by the National Land Transport Fund and the Provincial Growth Fund, has allocated $13.5 million to treat some of the ‘resilience hot spots’ between Gisborne and Potaka. The works include traditional engineering techniques such as retaining walls, coastal protection and improved drainage, as well as native planting programmes to help stabilise some of the significant slip and subsidence sites (places where the road is sinking) on the highway.
How do we strengthen, repair or stabilise a resilience hot spot?
We are combining traditional engineering techniques like retaining walls, rock protection and improved drainage with a native planting programme.
A more detailed rundown of possible resilience treatment options
What can communities expect over the coming construction season
Our teams have been working through assessments, designs, consents and construction planning for around 14 sites up the coast.
The summer construction season kicks-off in October and continues until around March and will see the SH35 resilience project get back underway as well as emergency works associated with the weather events.
Traffic management will be in place along SH35 and Waka Kotahi is working closely with our partners to minimise disruption.
COVID and the recent weather events have impacted the timing of the project, however the next two construction seasons are where we will see the significant spend happening.
What are the key sites for this season?
Five sites are planned for completion in 2022/2023 financial year:
1. SH35 Kopuaroa Hill: Subsidence retreat.
2. SH35 Busby’s Hill: Soil removal to stabilise slope and installation of retaining wall.
3/4. SH35 Turihaua Point and Pouawa: Rock protection.
5. SH35 Pakarae: Native planting (Complete).
Three of these sites (Busby’s Hill, Kopuaroa Hill and Turihaua Point coastal erosion) were severely affected by the March 2022 rain event.
