Volcanic Rim Ecological Restoration

Sumner Road, Christchurch


Following the 2011 Christchurch earthquake sequence, the road connecting Lyttelton to Sumner suffered immense destruction due to unprecedented rockfall and cliff collapse. In 2015, the Christchurch City Council (CCC) and New Zealand Transport Agency (NZTA) made the decision to reopen the road, undertaking a project of enormous scale.

In 2018, geotechnical rope access teams were required to scale the cliff face, removing loose rocks to protect the road rebuild. Unfortunately, the impact of this scaling operation destroyed a high percentage of the existing vegetation below, leaving only remnants and exposed soils. CCC commissioned a catch-bench design that would act as a first line of defence in preventing rockfall onto the new road below.

In order to rebuild the road, consent conditions required negative environmental impacts, caused by the construction project, to be offset. Red Tree, specializing in post-natural disaster ecological restoration, were approached and contracted to manage erosion, stabilize the land, and remediate the ecology above Sumner Road. Flax comprises a high percentage of the plantings in high risk rockfall zones and at maturity (as witnessed in other red zone sites), act as a second line of defence in preventing rock escape onto Sumner Road.

"Red Tree, specializing in post-natural disaster ecological restoration, were approached and contracted to manage erosion, stabilize the land, and remediate the ecology above Sumner Road."

The Challenge:

The topography was the major challenge Red Tree faced in this project; the elevated gradients and unstable terrain of the volcanic rim resulted in strenuous working conditions. Vigorous health and safety protocols had to be upheld in order to mitigate the risk to the multiple contractors onsite. In addition, a high population of possums within the restoration area posed a significant risk to native establishment.

In order to deliver the traditional planting phase of the project, native plants had to be brought onsite and distributed along the hillside. The difficult access and steep terrain made this very challenging for our team. At first, Red Tree Plant Technicians carried plants manually up the slopes; however, we quickly learned that the risk of physical stress and fatigue had to be mitigated.

The Solution:

A land stabilization Enviroblanket® was applied pneumatically across the exposed area below the catch-bench for rapid establishment of exotic grass species. Compost was used to boost substrate nutrients, provide erosion control, and to filter sediment runoff. This process required anchor points to facilitate rope access across the work site and to scale vertical faces between regions.

Following on from the Enviroblanket® application, Red Tree was contracted by CCC to traditionally establish ~25,000 plants along Sumner Rd. Teams of Red Tree Plant Technicians, trained in rope access, completed the planting and worked closely with McConnell Dowell, Golder Associates, and Boffa Miskell for traffic management, rockfall risk mitigation, and biosecurity respectively.

Geovert installed a rockfall risk mitigation fence below the working areas to act as a third line of defence in preventing rocks falling onto the road below. This meant the road could remain open while Red Tree undertook ongoing planted maintenance.

Challenging access and the necessity to reduce fatigue required Red Tree to come up with an innovative method of transporting native plants up the hillside. After considering various options, it was decided that the plants would be airlifted. Way2Go Heliservices commenced the airlift, delivering the plants in one tonne customised bags and positioning them along the hillside ready for planting.


The disturbed area below the cliff face, where the Enviroblanket® was applied, was transformed from a harsh rocky incline to being 100% vegetated and stable within three weeks post-application.

To date, no rocks have breached the installed rockfall prevention fence.

It is very satisfying to see the planted natives establishing well with minimal losses. Ongoing maintenance will allow for hand releasing, infill planting, and pest animal control guaranteeing the restoration project’s continuing success.

The road is now open and is one of Canterbury’s most iconic drives. The revegetation works undertaken by Red Tree not only re-established biodiversity but also added aesthetic and ecological value to the area; the surrounding landscape is now green and aesthetically beautiful.