Inspection and Maintenance: Enhanced Swales

From LID SWM Planning and Design Guide
Jump to navigation Jump to search
Inspection & Maintenance Guidance of enhanced swales, which are a vegetated stormwater best management practices that contains gently sloping open channels featuring a parabolic or trapezoidal cross-section and check dams, designed to both convey and treat stormwater runoff temporarily before entering the storm system (TRCA, 2016[1])

Overview[edit]

Enhanced swales are gently sloping vegetated open channels featuring a parabolic or trapezoidal cross-section and check dams, designed to convey and treat stormwater runoff (i.e., rainwater or snowmelt from roofs or pavements). The grading, Check dams and vegetation spreads out and slows down the flow of water, allowing suspended sediment and floatables (e.g., trash, natural debris, oil and grease) to settle out. A portion of the flowing water soaks into the soil and replenishes groundwater or is taken up by plant roots and evaporated back to the atmosphere. Runoff water is delivered to the practice through inlets such as curb cuts, spillways or other concrete structures, sheet flow from pavement edges, or pipes connected to catchbasins or roof downspouts. The planting bed and side slopes are typically covered with grasses or a mixture of flood tolerant, erosion resistant vegetation and stone. They do not feature filter media soil and sub-drains like bioretention or bioswales do. Water not ponded behind check dams or absorbed by the planting bed is conveyed to an adjacent drainage system (e.g., municipal storm sewer or other BMP) at the lowest downstream point by an outlet structure (e.g., ditch inlet catchbasin, culvert). Key components of this feature are described in further detail below.

Properly functioning enhanced swales reduce the quantity of pollutants and runoff being discharged to municipal storm sewers and receiving waters (i.e., rivers, lakes and wetlands). In addition to their SWM benefits, enhanced swales provide aesthetic value as attractive landscaped features.

Key components of Enhanced swales to pay close attention to are the:

Trash, debris and sediment builds up at these locations and can prevent water from flowing into or out of the practice.

Associated Practices[edit]

  • Bioretention cell: A flat-bottomed, depressed planting bed containing filter media soil, a gravel water storage layer and optional sub-drain pipe(s); Also known as a rain garden.
  • Stormwater planters: A bioretention cell contained within an engineered (e.g., concrete) structure.
  • Biofilter: Bioretention cell or swale with an impermeable liner or containment structure and sub-drain.
  • Bioswale / Dry swale or Bioretention swale: A gently sloping, linear oriented bioretention practice designed to be capable of conveying water across an elevation gradient. Also known as a bioswale or dry swale.
  • Stormwater Tree Trenches: Linear tree planting structures that feature supported impermeable or permeable pavements that promote healthy tree growth while also helping to manage runoff. Consist of subsurface trenches filled with modular structures and growing medium, or structurally engineered soil medium, supporting the overlying sidewalk.
  1. TRCA. 2016. Fact Sheet - Inspection and Maintenance of Stormwater Best Management Practices: Enhanced Swales. https://sustainabletechnologies.ca/app/uploads/2018/02/Enhanced-Swales-Fact-Sheet.pdf