Enhanced swales subtly capture and treat stormwater
As part of the permitting process, the Tennessee Department of Environment and Conservation mandates the City of Kingsport offer educational and outreach activities regarding stormwater, the city’s various control measures and why those measures are important to the general public.
The following article discusses the two types of swales and how each one captures and treats stormwater.
Enhanced swales, also called water quality swales, are a type of Stormwater Control Measure (SCM) designed to capture and treat stormwater from small storms using low check dams to slow or contain runoff. They are usually shallow, wide, and vegetated to help filter stormwater runoff.
There are two types of enhanced swales.
- Dry enhanced swales are broad and shallow with thick grass. They typically have an underdrain system designed to let stormwater filter through the bottom of the swale.
- Wet enhanced swales are designed to retain water and may have marshy conditions that support wetland vegetation. They are generally used in areas with a high-water table or poorly draining soils. Sediment and other pollutants settle to the bottom of the swale where they can be easily removed.
Most enhanced swales have the same basic components to help them function properly, including:
- Inlets – allow stormwater to flow into the swale.
- Pretreatment areas – rock or vegetated areas which prevent trash and debris from entering the channel.
- Channel – where stormwater is collected. Low flows are slowed by the check dams, while high flows go over the check dams.
- Underdrain – lets water that has soaked into the soil exit the swale.
- Check dams – rock berms perpendicular to the flow path that slow water in the swale, providing treatment of polluted stormwater.
- Outlet structure – allows water to exit the swale in a controlled way.
Swales may be inspected by the local municipality to ensure they are functioning correctly. However, all maintenance is the responsibility of the property owner.
In order for a swale to work efficiently, vegetation should be mowed at least twice a year and the vegetation should be thick and healthy and not include shrubs or trees. All trash, debris and sediment should be removed at regular intervals. Any areas of erosion should be repaired.
The outlet structure should also be free of mud, debris and trash. Inlets should be checked for clogs and erosion. The swale should be observed during and after rain events to ensure it is functioning properly.
If you have a concern about a specific swale in Kingsport, you may call Water Services at 423-229-9454. You can also report any possible issues by using the ConnectKingsport app.
