Swales are depressions that follow the contour around the base of a slope (natural or created), channeling storm water from one place to another. They filter runoff along the way by allowing it to sink into the soil. Plants on a swale’s gently sloping banks—and sometimes down the center of the channel itself—take up much of this water. Fast-draining soil is also key. The addition of a perforated pipe laid in gravel underneath can help handle heavy water flow.
A small swale might carry gutter water from a house to a dry well, while a more substantial one could run along the base of a hill above a low-lying house to divert water around it. Jan Johnsen, a landscape designer in Mount Kisco, New York, often landscapes swales by lining them with river rock. Along the sides, she uses evergreen ferns, sedges, winterberry, grasses, and Siberian and Louisiana irises that thrive in moist conditions. Rugged prairie plants or other natives that are at home in fast-draining soil are another option.