Swales follow the contours around the base of a natural or created slope, redirecting storm water and filtering runoff as it sinks into the soil, instead of keeping it in one place, like a rain garden. Plants suck up the water along a swale’s gently sloping banks and sometimes down the center of the channel. Fast-draining soil maximizes drainage efficiency, and perforated pipe underneath the gravel can help with heavy water flow.
Small swales can direct gutter water to a dry well, while more substantial ones could run along the base of a hill to divert water around a low-lying house. Jan Johnsen, a landscape designer in Mount Kisco, New York, landscapes swales with a river rock lining and plants that thrive in moist conditions along the sides: evergreen ferns, sedges, winterberry, grasses, and Siberian and Louisiana irises. She also uses rugged prairie plants or other natives to fast-draining soil.