swales

Swales are shallow, broad channels used to manage surface runoff by directing it along a landscape or infrastructure corridor. They are typically designed to intercept rainfall runoff, promote infiltration, and reduce erosion on slopes or permeable surfaces. Swales may be vegetated with grasses or other groundcovers to enhance filtration and stability, or they may be minimally lined trenches mainly for conveyance.

Common types include surface or vegetated swales, often called bioswales when planted and engineered for water quality, infiltration swales that encourage percolation into the soil, and dry or wet swales that seasonally hold water. Some designs incorporate a stone outlet, check dams, or sediment traps to capture debris and slow flows.

Design considerations involve local climate, soils, and expected runoff. Important factors include the soil infiltration rate, slope, and swale cross-section (width, depth, and side slopes), as well as inlet and outlet controls to prevent overtopping. Plant selection favors deep-rooted, erosion-resistant vegetation; maintenance requirements depend on sediment buildup and vegetation health.

Swales provide multiple benefits, including reduced peak flows, increased infiltration and groundwater recharge, improved water quality through filtration and sediment capture, and habitat and aesthetic value. They are widely used in urban and agricultural settings as a low-cost component of green infrastructure and erosion control programs.

Limitations and challenges include clogging from sediment or excessive vegetation, reduced effectiveness on very flat or poorly infiltrating soils, and the need for regular maintenance. In some climates they may thaw or freeze differently; design should consider safety and access for maintenance equipment.