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Green Mulch

Hammerton Lane, Heathcote, Christchurch
Area: 4100m2
Date: June 2016

Backstory

During the Christchurch earthquake of 2011, houses perched on Hammerton Lane were subjected to boulder roll from the hills above.

Subsequently, the site was red zoned and five home owners settled with the Crown. The houses were then demolished and the land recontoured. This site had a specification of 450 gsm coconut fibre erosion control matting secured with bio degradable ground staples at 1.5 centres and planted specimen at 1.5 spacing’s.

Challenges

A large and steep site containing a mix of virgin clay cuts and back fill zones with a 1-2 1-3 gradient requiring some rope access work to install the matting and plants.
Challenges associated with this topography were the water catchment and stormwater sheet flow potential and its associated sediment run off, plus development and progression of rilling. The coconut matting in the face of the scale and gradient of the site needed reinforcing, especially in a possible weather event.

Solutions

For fast slope stabilization, we needed a quick germinating ground cover. the best way to stabilize a slope is to establish root mass as quickly and cost effectively as possible. Red Tree’s solution to these environmental conditions was to speed seed a green mulch cover crop directly after the completion of planting.
An appropriate clover species was selected for the task for the following reasons:

  • Toleration of clay soil
  • Performance in drought conditions
  • Ability to overcome competition from exotic weeds species
  • Grows no higher than 30 cm

The clover germinated within four weeks and colonized within six months; it has delivered beyond our expectations.

Our Outcome

A very successful trial with the clover species establishing as a green mulch to bind soil and clay thus assisting to reduce riling, sheet flow erosion and sedimentation with the added benefits of weed suppression, nitrogen fixing and because of the uniformity of its colour and texture over the site it has the added bonus of delivering aesthetic value.