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.