Generally grassed swales are used to treat relatively small drainage areas of five acres or less. In highly urbanized areas or other highly impervious areas grass swales are not recommended unless constructed in series or function as pretreatment for other stormwater management practices.

Are swales necessary?

Swales, like any catchment, are a means of stopping water runoff, especially from roads and hard surfaces, and putting it to use rather than having it drain away. Using swales for these reasons can prevent both floods and droughts, which make them a pretty powerful tool.

What is the purpose of a swale?

For many years they have been used along rural highways and residential streets to convey runoff. Today, swales not only convey stormwater but also help to treat runoff to reduce pollutants. Like ditches, swales collect stormwater from roads, driveways, parking lots and other hard surfaces.