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Erosion Control On Difficult Terrain

Sumner Catch Bench
Area: 4500m
Date: November 2017

Backstory

The brief was to remediate the shelf ecology above Sumner Road affected by the earthquake and post-quake debris. The shelf contained considerable biodiversity that needed restoration.

Below the road there was considerable erosion debris that needed greening to improve aesthetic value. The Enviroblanket has proven to revitalize latent biodiversity by restoring soil ecology to necessary for thriving plant communities.

The Challenges

The Sumner Road site contains extreme gradients with potential rock fall hazards. the Enviroblanket application was tackled using rope access. Red Tree installed rock bolt anchors and expansion bolts with hangers as anchor points to facilitate access across the work site, scaling vertical faces between ecological regions.

All round a high clearance site requiring a comprehensive Health and Safety Policy to work in this location. Surrounding hazards included use of explosives, heavy earth moving machinery, and cliff face collapse. To reduce risk exposure, the Enviroblanket was the one pass solution that does not require further maintenance.

Photo Below Left: Below Sumner Catch Bench before remediation.

Photo Below Middle: Below Sumner Catch Bench after remediation. Results after 6 weeks, Clover and Rye establishing.

Photo Below Right: Enviroblanket™ application above Catch Bench.

The Solution

Above the Catch Bench Red Tree, with industry partner Canterbury Wood Chip, used the catch bench platform below the shelf to deliver an engineered compost blend to the work face. Below the Catch Bench A seeded 25mm Enviroblanket was applied to green the disturbed slope littered with debris from blasting.

Seeded with clover and perennial rye grass, the Enviroblanket provided rapid stabilization and moisture retention for the cover crops to establish. Verticle Enviroblanket to address the cut clay faces, Red Tree applied a customised high fines Enviroblanket mix into the existing geotextile pinned to the cut faces with a clover and rye grass cover crop seed mix.

  • Compost provides initial nutrient ‘boost’ for germinated seed.
  • Seed and tackifier is mixed and applied in one pass.
  • Compost has better erosion control properties than a conventional hydroseed.
  • Use of compost socks will help reduce and disperse channel flow area within gullies/ water course areas.

Our Outcome

Above the Catch Bench, initially the compost fines and natural ground water caused phenomenal amount of regeneration and the species already there such as flax, mahoe, ferns as well as grasses. Native species planted in root trainer grades, showed great heath and vigor. No further erosion from the shelf has occurred.

Below the Catch Bench Enviroblanket achieved germination within 8 days of application with clover and perennial rye grass. After 8 weeks there was significant root mass development and greening of the slope. The slope has remained thriving and vibrant through Christchurch’s summer low rainfall.

This one pass solution has been a success due to moisture retention and rapid vegetative cover even on this very bony site.

When it comes to vertical faces the EnviroblanketTM blend requires a three-dimensional geo textile matrix to stabilize it and hold it in place. Once this is achieved rapid vegetation cover is able to be established.