swale

A swale is a low or hollow feature in the landscape, typically elongated and following the slope of the terrain. It functions as a channel to collect and convey surface water, and may be seasonally wet or persistently moist depending on climate and subsurface conditions. Swales can form natural part of a drainage network or occur as remnants of ancient landforms.

Natural swales occur in a variety of settings, including hillside slopes, valley floors, river terraces, and glacial landscapes. They often host wetland or meadow vegetation and provide habitat for plants and animals. Their shape and size vary, but they are generally longer and narrower than broad depressions and can transition between dry and wet states with seasonal changes.

In landscape architecture and urban design, artificial swales componentize sustainable stormwater management. A bioswale or vegetated swale is a shallow, open-channel drainage feature lined with soil and plants that slows runoff, promotes infiltration, and filters pollutants before water reaches storm sewers or receiving waterways. Design considerations include depth, width, slope, soil mix, and plant selection; a berm on the upslope side helps capture runoff and reduces erosion.

Swales are contrasted with simple drainage ditches by their ecological and hydraulic function; they are intended to manage water thoughtfully while supporting vegetation and habitat. They are used in green infrastructure, rainwater harvesting, site rehabilitation, and erosion control projects.