Bioswales

This article is about installations designed to capture and convey surface runoff along a vegetated channel, whilst also promoting infiltration.
For underground conveyance which promotes infiltration, see Exfiltration trenches.
For design recommendations on grassed channels, see Enhanced grass swales.

Overview

The fundamental components of a bioswale are:

• A graded channel
• Planting
• Filter media, to permit infiltration into the facility (not necessarily to soils below)

Additional components may include:

• Underdrain with clean out and inspection ports
• Impermeable membrane to prevent infiltration to soils below
• Check dams to facilitate short tern ponding

Design

Swales: Sizing

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

The slow movement of water into or through a soil or drainage system.

Penetration of water through the ground surface.

Linear bioretention cell designed to convey, treat and attenuate stormwater runoff. The engineered filter media soil mixture and vegetation slows the runoff water to allow sedimentation, filtration through the root zone, evapotranspiration, and infiltration into the underlying native soil.

Cleanouts are "a fitting access in a drainage system or venting system that is installed to provide access for cleaning and inspection and that is provided with a readily replaceable air tight cover" (O.Reg 332/12: Building Code, 2022).

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.