A "V" Drain, approximately 300 metres long, was cleared of all vegetation and prepared using standard civil engineering practices (without compaction). Two stabilising methods were compared along the length of the drain.
Method 1 - Standard construction
When the drain was prepared a 100m section was allocated at the first part of the drain flow. They applied traditional construction methods using silt fencing and silt bags filled with sand. The section was treated with Rye Grass Seeds and Bitumen to stabilise the soil.
Method 2 – Bioaction recommended construction
The second 200m section was prepared using the same clearing and reshaping process. The drain was then covered with CoirNet along the length of the drain to its 2m width. It was then pinned with 1m centres using “U” shaped soil pins. FiltaBooms were placed across the drain at 20m intervals and pined to the soil through the coir netting in a “V” shape to trap floating solids in the valley. This section was then treated with the same Grass & Bitumen application as the first section.
The traditional construction (method 1) had shown deep scouring and erosion, particularly the loose uncompacted soil common through the entire drain. The soil retention applications such as silt fence and silt bags were damaged or relocated by the energy of the stormwater flow. All the grass applied was lost with the loss of soil.
In contrast the second section (method 2) showed no damage even though the stormwater would have had greater energy and carried all the soil scoured from the upstream section. It retained the soil and sediment from the first section, and the grasses were well established with the roots system stabilised by the retained moisture in the CoirNet.
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