Conveyance and End-of-Pipe Measures for Stormwater - FCM

Table 4–1a: Application of Conveyance Control Best Management Practices (continued)
Grassed or Vegetated Swales
Application
Requirements
Opportunities and
Limitations
Proven Effectiveness
They are primarily applicable for new or redevelopment areas with appropriate physical
conditions. Infiltration or filtration requires an area with pervious soils (generally,
an infiltration rate of > 15 mm/hr), bedrock and water table > 1 m below bottom
of swale, and slope between 0.5% and 5% in the direction of flow.
Opportunities identified are based on new development or redevelopment areas
with suitable soil conditions. Opportunities are also identified by the size of the drainage
area (< 15 ha) and the condition of roads and existing sewer pipes in the area.
More economical to be considered with the reconstruction of roads.
Effective in low-grade areas, pervious soils, and for relatively short length. Most
effective with a channel slope between 1% and 2%, a bottom width of min. 750 mm
and grass height 75 mm. Low-gradient swales with check dams have slightly higher
removal rates than high-slope swales without check dams.
Cost Capital cost: low. Operation and maintenance costs: low.
Pervious Pipe Systems
Application
Requirements
Opportunities and
Limitations
Proven Effectiveness
Small drainage area (< 6 ha). Pre-treatment of road runoff may be required. Require
areas with pervious soils (minimum infiltration rate of 15 mm/hr), bedrock and water
table > 1 m below bottom of drainage media, slope between 0.5% and 5% (ideally 1%
to 2%) in the direction of flow. Minimum setback from building foundations: 3 m down
gradient (towards the building) and 30 m up gradient (away from the building). Not
suitable in locations receiving large sediment loads.
Opportunities identified based on the presence of certain surface features, and
the condition of the roads and existing sewer pipes in an area. More economical
to be considered with the reconstruction of roads.
Few applications in Ontario. These systems are experimental and clogging problems
have been experienced.
Cost Capital cost: high. Operation and maintenance costs: medium.
Pervious Catch Basins
Application
Requirements
Opportunities and
Limitations
Proven Effectiveness
Small drainage area (< 6 ha). Not suitable in locations that receive a large sediment load
that could clog the pre-treatment system. Pre-treatment of road runoff may be required.
New or redevelopment area with pervious soils (minimum infiltration rate of 15 mm/hr),
and bedrock and water table > 1 m below bottom of drainage media.
Opportunities identified based on the presence of certain surface features,
and the condition of the roads and existing sewer pipes in an area, also by the project
catchment area (< 15 ha). More economical to be considered with the reconstruction
of roads.
As with pervious pipe systems, varying results have been reported. Problems would
result from poor design, poor construction practices, poor site physical conditions,
or inadequate stabilization of development before construction.
Cost Capital cost: high. Operation and maintenance costs: medium.
Conveyance and End-of-Pipe Measures for Stormwater Control — July 2005 35
4. Applications and
Limitations
4.4 Management
Practices
Table 4–1a
Application of Conveyance
Control Best Management
Practices (continued)