Green swales reduce pollution. Salix worked with Balfour Beatty and the Highways Agency to create a highly effective large scale SuDS project for 18 km along the side of the A11.
The new soft engineered ‘Green Swale Grass Channel’ attenuates road runoff water, filters suspended solids, and traps hydro carbons and heavy metals, significantly improving water quality.
Due to the presence of special protection aquifers in this area of the A11, the Highways Agency’s environmental statement required a green drainage solution to slow the flow of water and help cleanse hydrocarbons, salt and other road pollutants carried by the water before it reached the soakaways.
Robust scour proof erosion control
HydraCX and TerrAffix products, a hydraulic erosion control solution, was sprayed onto a Type 1 fill. This was used as it has been tested in extreme environments and ensured rapid vegetation of the drainage channels.
A tough grass selection was added to the straw, cotton, polymer and tackifier mix, these plants could withstand the level of pollution being washed off the road.
A surface erosion control blanket of biodegradable coir – Bionet C125BN – was installed over the top of the HydraCX to prevent scour erosion during storm events.
These erosion control blankets are designed to provide immediate erosion protection and vegetation establishment assistance, they then degrade after the root and stem systems of the vegetation are mature enough to be stable and withstand heavy flows of water.