The most common stormwater treatment, swales range from irrigation ditches to engineered systems. Similar in form to a natural stream channel, swales are commonly protected from erosion by a layer of riprap (stone), and underlain with a geotextile filter fabric.

The swale tested here is not to be confused with engineered systems known as water quality swales, which are designed with internal drainage or check dams. State design criteria specify slopes of typically less than one percent, and flow velocities of less than one foot per second for a 10-year storm.

Maintenance demands involve standard landscaping, primarily periodic mowing. Many swales are designed to function as dry systems. Often, however, they collect water due to vegetation and lack of proper maintenance.

Our first year of testing this approach focused on a stone-lined swale; in year two we will examine a vegetated swale; and in year three, a vegetated swale retrofitted with engineered filter berms.