A grass swale is a linear, shallow channel that allows vegetation of flood-resistant plants. The design looks to carry stormwater at a slower, controlled rate to both slow and clean stormwater acting as a filter to remove pollutants while also allowing infiltration.
Unlike a normal ditch, a swale is shallow and relatively wide in order to reduce peak flows. They are often located close to the source of runoff and can be used to link other SuDS functions such as ponds and wetlands.
Swales should be set up with a small fall – performances can be improved by placing dams along the length – this will reduce flow rates further which will reduce erosion risks.
Utilising Grass Swales
A swale is dry during dry weather but in wet weather, rainwater flows into it along its length and moves slowly through the channel.
Step-by-step guide to using Grass Swales
- During dry weather the swale is dry but when wet rainwater will flow along the swale slowly and infiltrating into surrounding grassy areas.
- Surface water flows are slowed as rainwater flows away
- Sediment gets held and deposited with pollutants broken down in the soil and vegetation
- Overflow areas can be created – this will allow greater room for storage during particularly heavy rainfalls
- Between rainfall events, the swale should dry out
- Maintenance is minimal, but the grass should be cut to ensure that the swale is operating efficiently
If you are looking for assistance with a grass swale project then we can help. Get in touch today.
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