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|For simple downspout disconnection the roof drainage area should not be greater than 100 square metres
|For simple downspout disconnection the roof drainage area should not be greater than 100 square metres
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|Sand or other granular materials should not be applied as anti-skid agents during winter operation because they can quickly clog the system. Winter maintenance practices should be limited to plowing, with de-icing salts applied sparingly
|Sand or other granular materials should not be applied as anti-skid agents during winter operation because they can quickly clog the system. Winter maintenance practices should be limited to plowing, with de-icing salts applied sparingly
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![[Enhanced Grass Swales]]
![[Enhanced Grass Swales]]
|Grass swales usually consume about 5 to 15 percent of their contributing drainage area. A width of at least 2 metres is needed
|Site topography constrains the application of grass swales. Longitudinal slopes between 0.5 and 6% are allowable. This prevents ponding while providing residence time and preventing erosion. On slopes steeper than 3%, check dams should be used
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|Grass swales can be applied on sites with any type of soils
|To protect groundwater from possible contamination, source areas where land uses or human activities have the potential to generate highly contaminated runoff should not be treated by grass swales.
|"Enhanced grass swales should be located a minimum
of four (4) metres from building foundations to prevent water damage."
|Utilities running parallel to the grass swale should be offset from the centerline of the swale. Underground utilities below the bottom of the swale are not a problem.
|The conveyance capacity should match the drainage area. Sheet flow to the grass swale is preferable. If drainage areas are greater than 2 hectares, high discharge through the swale may not allow for filtering and infiltration, and may create erosive conditions. Typical ratios of impervious drainage area to swale area range from 5:1 to 10:1.
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|Designers should ensure that the bottom of the swale is separated from the seasonally high water table or top of bedrock elevation by at least one (1) metre
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![[Dry Swales]]
|Dry swale footprints are approximately 5 to 15% of their contributing drainage area. When applied to residential areas, the swale segments between driveways should be at least 5 metres in length.
|Dry swales should be designed with longitudinal slopes generally ranging from 0.5 to 4%, and no greater than 6% (PDEP, 2006). On slopes steeper than 3%, check dams should be used.
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|Dry swales can be located over any soil type, but hydrologic soil group A and B soils are best for achieving water balance benefits. Facilities should be located in portions of the site with the highest native soil infiltration rates. Where infiltration rates are less than 15 mm/hr, an underdrain is required
|To protect groundwater from possible contamination, source areas where land uses or human activities have the potential to generate highly contaminated runoff should not be treated dry swales designed for full or partial infiltration. Facilities designed with an impermeable liner can be used to treat runoff from pollution hot spots
|Dry swales should be setback four (4) metres from building foundations. When located within 3 metres of building foundations, an impermeable liner and perforated pipe underdrain system should be used.
|Designers should consult local utility design guidance for the horizontal and vertical clearance between storm drains, ditches, and surface water bodies. It is feasible for on-site utilities to cross dry swales; however, this may require the use of special protection (e.g., double-casing) for the subject utility line.
|Dry swales typically treat drainage areas of less than two hectares. If dry swales are used to treat larger areas, the velocity through the swale becomes too great to treat runoff or prevent erosion. Typical ratios of impervious drainage area to dry swale area range from 5:1 to 15:1.
|Facilities receiving road or parking lot runoff should not be located within two (2) year time-of-travel wellhead protection areas.
|Designers should ensure that the bottom of the swale is separated from the seasonally high water table or top of bedrock elevation by at least one (1) metre to prevent groundwater contamination
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![[Perforated Pipe]]
|Perforated pipe systems should be located below shoulders of roadways, pervious boulevards or grass swales where they can be readily excavated for servicing. An adequate subsurface area outside of the four (4) metre setback from building foundations and suitable distance from other underground utilities must be available
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