Both Filter Strips and Swales are designed to mimic natural drainage patterns by allowing rainwater to run in sheets through vegetation, slowing and filtering the flow. Swales can also be designed for a combination of conveyance, infiltration, detention and treatment of runoff dependent upon individual site requirements.
Swales are usually designed as conveyance systems, but can also be designed with check dams to increase attenuation and, where viable (ground conditions permitting), infiltration. Filter strips only attenuate the flow slightly but they can be used to reduce the drained impermeable area.
Swales and filter strips are effective at removing polluting solids through filtration and sedimentation. The vegetation traps organic and mineral particles that are then incorporated into the soil, while the vegetation takes up any nutrients.
Swales and filter strips are often integrated into the surrounding land use, for example public open space or road verges. Swales can also provide a wildlife habitat which in urban developments can be a key improvement.
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