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Line 86: − ''Note Site Considerations from the Bioretention Fact Sheet [https://sustainabletechnologies.ca/app/uploads/2013/02/Bioretention.pdf] in the 2010 CVC/TRCA LID Stormwater Management Planning Design are detailed below and within links included'' Line 98:
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→Planning considerations
==Planning considerations==
==Planning considerations==
===Infiltration===
===Infiltration===
Where infiltration is infeasible or not permitted, but the design calls for planted landscaping, try a [[stormwater planter]] instead.
Where infiltration is infeasible or not permitted, but the design calls for planted landscaping, try a [[stormwater planter]] instead.
===Space===
===Native Soil===
Bioretention can be constructed over any soil type, but hydrologic soil group A and B are best for achieving water balance objectives. Facilities designed to infiltrate water should be located on portions of the site with the highest infiltration rates. For infiltration rates <15 mm/h an underdrain is recommended. Native soil infiltration rate at the proposed location and depth should be confirmed through in-situ measurements of hydraulic conductivity under field saturated conditions.
===Wellhead Protection===
Facilities receiving road or parking lot runoff should not be located within 2 yr time-of-travel Wellhead Protection Area (refer to drinking water source protection plan).
===Available Space===
*Reserve open space equal to roughly 10 to 20% the size of the contributing drainage area.
*For optimal performance bioretention facilities should receive runoff from impervious drainage areas between 5 to 20 times their own permeable footprint surface area.
*For optimal performance bioretention facilities should receive runoff from impervious drainage areas between 5 to 20 times their own permeable footprint surface area.
*In the conceptual design stage it is recommended to set aside approximately 10 - 20 % of the contributing drainage area for bioretention facility placement.
*In the conceptual design stage it is recommended to set aside approximately 10 - 20 % of the contributing drainage area for bioretention facility placement.
*Proximity to underground utilities and overhead wires: Consult with local utility companies regarding horizontal and vertical clearance required between storm drains, ditches, and surface water bodies. Further, check whether the future tree canopy height in the bioretention area will not interfere with existing overhead wires.
*Proximity to underground utilities and overhead wires: Consult with local utility companies regarding horizontal and vertical clearance required between storm drains, ditches, and surface water bodies. Further, check whether the future tree canopy height in the bioretention area will not interfere with existing overhead wires.
The principles of bioretention can be applied in any scenario where planting or vegetation would normally be found.
The principles of bioretention can be applied in any scenario where planting or vegetation would normally be found.
===Site Topography===
Contributing slopes should be 1 to 5%. The filter bed surface should be flat to allow flow to spread out. A stepped, multi-cell design can also be used.
===Available Head===
If an underdrain is used, then an elevation difference of 1 to 1.5 m is needed between the inverts of the inlet and the downstream storm sewer.
===Water Table===
Maintaining a separation of 1 m between the elevations of the bottom of the practice and the seasonally high water table, or top of bedrock, is recommended. Lesser or greater values may be considered based on [[groundwater]] mounding analysis.
===Pollution Hot Spot Runoff===
To prevent groundwater contamination, runoff from pollution hot spots should not be treated by bioretention facilities designed for full or partial infiltration. Filtration only facilities (with an impermeable liner) can be used.
===Proximity to Underground Utilities===
Designers should consult local utility design guidance for the horizontal and vertical clearances required between storm drains, ditches, and surface water bodies.
===Karst===
Infiltration designs are unsuitable in areas of known or implied karst topography and geologic formations.
===Overhead Wires===
Check whether the future tree canopy height in the bioretention area will interfere with existing overhead wires.
===Setbacks From Buildings===
If an impermeable liner is used, no setback is needed, although designing to maintain drainage away from the building is crucial. Where no liner is used, a setback of 4 m from the building foundations should be applied.
===Private sites===
===Private sites===
In single family residential sites [[Rain gardens|rain gardens]] most often take the form of a soft edged, traditional perennial planting bed.
In single family residential sites [[Rain gardens|rain gardens]] most often take the form of a soft edged, traditional perennial planting bed.
As many private industrial, commercial and institutional sites have landscaping around their [[Bioretention: Parking lots| parking lots]], bioretention is an increasingly popular choice to manage stormwater in these contexts.
As many private industrial, commercial and institutional sites have landscaping around their [[Bioretention: Parking lots| parking lots]], bioretention is an increasingly popular choice to manage stormwater in these contexts.
===Streetscape===
===Streetscape===
Bioretention is a popular choice for making urban green space work harder. Design configurations include extending the cells to accommodate shade trees, and using retrofit opportunities to create complete streets with traffic calming and curb extensions or 'bump outs'. See [[Bioretention: Streetscapes]]
Bioretention is a popular choice for making urban green space work harder. Design configurations include extending the cells to accommodate shade trees, and using retrofit opportunities to create complete streets with traffic calming and curb extensions or 'bump outs'. See [[Bioretention: Streetscapes]]