RST Environmental Solutions Ltd

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Bio-engineering uses plants and trees to create engineered structures for slope failures, dropouts and stream restorations. Poplars and willows are generally preferred as they offer many characteristics that natives do not in the early stages.

Poplars and willows establlish quickly, have good root penetration and high water uptake. This is particularly important in the first year, as the roots create a cohesive force in the soil and uptake large amounts of water to stop further movement of the failure.

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Taramakau Settlement Bioengineering: Before & 5 months later

Even if a native system is to be established it is common to include willows and poplars in the planting matrix as they can be removed once the failure has stabilised. Therefore, the benefits of a fast growing system can be captured yet a native system can be the final outcome. The willows used are a shrub type growing to three-four metres in height, which do not sucker or grow from their root systems.

Pinning
Poplars are generally preferred for this system which is used on large scale failures, generally covering a hectare or more. The poles are planted as deep as possible at high density and drainage is also installed on the site to assist in removing water.

Brush-layering
The Brush-layer system is used for dropouts or where a reinforced earth wall needs to be made. Willow brush is used to form a matrix of stems across a pre-cut bench. This is then layered up and the dropout can be back-filled behind. Once the brush has been established, it can be cut back with a reach mower.

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Live Poledrains
These drains are formed by laying bundles of willows horizontally in a hand-dug dish channel, which is then partly covered with soil. The willows produce roots from the lower nodes and stem material from the upper ones.

Live Poledrains are ideal for sites where the wet area of a slip is inaccessible to machinery. A drain can be created and even if there is movement on the site, the willow poles will keep the flow running.

 

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