Exfiltration: Performance

Ability of exfiltration systems to meet SWM objectives

Water balance benefit	Water quality improvement	Erosion control benefit
Yes	Yes	Partial: depending on soil infiltration rate

Water balance

The degree to which water balance objectives are met will depend on the underlying native soil type on which the system is located. Several Ontario studies have assess the performance of exfiltration systems in cold climates.

Volumetric runoff reduction achieved by exfiltration systems

Practice	Location	Underlying soil type	Runoff reduction
Grass swale/perforated pipe	Nepean, ON	Silty till	73 %
Grass swale/perforated pipe	Nepean, ON	Sandy silty till	86 %
Perforated pipe	Etobicoke, ON	Clay/clayey silty till over silty sand	95 %
Perforated pipe	North york, ON	Silty sand	89 %

The downward movement of water through the soil, the downward flow of runoff from the bottom of an infiltration BMP into the soil.

Loss of water from a drainage system as a result of percolation or absorption into the surrounding medium (e.g., the infiltration of water into the native soil through a perforated pipe wall as it is conveyed).

Stormwater Management

The accounting of inflow and outflow of water in a system according to the components of the hydrologic cycle.

Includes the protection of soil from dislocation by water, wind or other agents.

The rate at which stormwater percolates into the subsoil measured in inches per hour.

The accounting of inflow and outflow of water in a system according to the components of the hydrologic cycle.

The natural ground material characteristic of or existing by virtue of geographic origin.

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 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.

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.

Vegetated, open channels designed to convey, treat and attenuate runoff. Design variations range from simple grass channels, which are designed primarily for conveyance to more complex treatment and volume reduction designs like enhanced grass swales, and dry swales or bioswales.

1. A mineral soil separate consisting of particles less than 0.002 millimeter in equivalent diameter. 2. A soil texture class. 3. (Engineering) A fine-grained soil (more than 50 percent passing the No. 200 Sieve) that has a high plasticity index in relation to the liquid limit. (Unified Soil Classification System).

Mineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm.

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.