Filter strips and filter drains
Filter strips and filter drains
Filter strips and filter drains are examples of source control. Source control measures deal with run-off at, or close to, the surface where rainfall lands. You may need to use additional sustainable drainage system (SUDS) components to control any overflow.
Filter strips
Filter strips are often used beside roads. The run-off passes across a strip of ground where some or all of it can soak away. The rest often enters a swale (shallow drainage channel) or another SUDS component. You can use this strip of ground to filter grit and other particles from the run-off.
Filter drains
You can use filter drains beside roads and other impermeable surfaces. These are also called filter trenches.
Run off that flows into the filter drain can soak away into the surrounding soil. The stone fill in the filter drain collects particles and helps prevent pollutants from entering the groundwater. You can use a filter strip or swale to reduce the level of pollutants entering the filter drain.
However, you should not use filter drains in areas such as busy road junctions, where there is a high risk of pollution occurring or where rainwater can become heavily contaminated.
You can use filter drains for source control, to manage run-off close to the surface where the rainfall lands, but you can also use them to convey run-off between SUDS measures.