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* Design storm duration, D (h)
* Design storm duration, D (h)
* Infiltration target for design storm event, I<sub>d</sub> (mm)
* Infiltration target for design storm event, I<sub>d</sub> (mm)
* Drainage time target to fully drain the active storage, t (h), based on long-term average inter-event period for the location or local criteria
* Drainage time t (h) to fully drain the active storage of the practice, based on provincial or municipal criteria or average inter-event period for the location
* Field infiltration rate of the underlying native soil f<sub>f</sub> (mm/h), median of field measurements or based on interpolation from median grain-size distribution results
* Field infiltration rate of the underlying native soil f<sub>f</sub> (mm/h), median of field measurements or based on interpolation from median grain-size distribution results
* Design infiltration rate of the underlying native soil f' (mm/h), median field measured value divided by a safety factor (z)
* Design infiltration rate of the underlying native soil f' (mm/h), median field measured value divided by a safety factor (z)
* Types of plants to be supported by the filter media bed (i.e. grasses vs. mix of grasses, plants and shrubs vs. trees)
* Types of plants to be supported by the filter media bed (i.e. grasses vs. mix of grasses, plants and shrubs vs. trees)
* How runoff will be delivered to the practice (i.e. to filter bed surface; to storage reservoir; or both)
* How runoff will be delivered to the practice (i.e. to filter bed surface; to storage reservoir; or both)
==Calculate the maximum overall depth==
==Decide if an underdrain will be included==
*Step 1: Determine what the planting needs are and assign appropriate depth of media, using the table above.
* Step 1: Based on the median infiltration rate of the native soil at 1.5 to 3 metres depth below the practice location, or interpolation from the median grain-size distribution results, decide if an underdrain will be included in the design.<br>
*Step 2: Select an underdrain perforated pipe diameter (typically 100 - 200 mm), assign this as an 'embedding' depth. *Note that this component does not apply if a downstream riser is being used to control an extended saturation zone.
If the median field infiltration rate of the underlying native soil is less than 15 mm/h, include an underdrain.
*Step 3: Calculate the maximum permissible storage reservoir depth beneath the underdrain perforated pipe (''d<sub>s, max</sub>'', mm):
<math>d_{s, max}=f'\times t \times 1/n</math>
==Select a surface ponding depth to begin sizing with==
* Step 2: Determine a maximum surface ponding depth (''d<sub>p, max</sub>'')
For practices without underdrains:<br>
<math>d_{p, max}=f'\times48</math>
{{Plainlist|1=Where:
*''f''' = Design infiltration rate (mm/h), and
*48 = Maximum permissible drainage time for ponded water (h)
*Note that in designs without underdrains, conceptually the drainage of ponded water is limited by infiltration through the base of the practice.}}<br>
For practices with underdrains elevated in the storage reservoir profile:
<math>d_{p, max}= depth of storage reservoir below invert of the underdrain perforated pipe.<br>
For practices with underdrain on base of the storage reservoir and connected to a riser (e.g., standpipe and 90 degree coupling):
d<sub>p, max</sub>= Difference between elevation of reservoir bottom and invert of the riser (i.e 90 degree coupling).<br>
* Step 3: Determine the design surface ponding depth, d<sub>p</sub>' (m) to begin sizing with<br>
For practices with soft (i.e. landscaped) edges and bowl-shaped ponding areas calculate the mean ponding depth:
<math>d_{p}'=d_{p, max}\divide 2
==Calculate the total depth of the practice, d<sub>T</sub>==
* Step 2: Calculate the active storage depth of the storage reservoir (''d<sub>s'', mm):<br>
For practices with no underdrain:<br>
<math>d_{s}=(f'\times t \times 1/n) + d{p}</math>
{{Plainlist|1=Where:
*''f''' = Design infiltration rate (mm/hr),
*''t'' = [[Drainage time]] (hrs). Check local regulations for drainage time requirements; and
*''n'' = Porosity of the reservoir aggregate}}<br>
For practices with an underdrain:<br>
<math>d_{s}=f'\times t \times 1/n</math>
{{Plainlist|1=Where:
{{Plainlist|1=Where:
*''f''' = Design infiltration rate (mm/hr),
*''f''' = Design infiltration rate (mm/hr),
*48 = Maximum permissible drainage time for ponded water (hrs)
*48 = Maximum permissible drainage time for ponded water (hrs)
*Note that in designs without underdrains, conceptually the drainage of ponded water is limited by exfiltration at the base of the practice.}}
*Note that in designs without underdrains, conceptually the drainage of ponded water is limited by exfiltration at the base of the practice.}}
* Step 2: Determine what the planting needs are and assign an appropriate depth of filter media, using the table above.
* Step 3: Select an underdrain perforated pipe diameter (typically 100 - 200 mm), assign this as an 'embedded' depth equal to the pipe diameter. *Note that this component does not apply if a downstream riser is being used to create the storage reservoir.
* Step 5: Sum total depth of bioretention components, and compare to available depth between the surface grade and the seasonally high water table or top of bedrock elevations.
* Step 5: Sum total depth of bioretention components, and compare to available depth between the surface grade and the seasonally high water table or top of bedrock elevations.
* Step 6: Adjust component depths to maintain a separation of 1.0 metre between base of the practice and seasonally high water table or top of bedrock elevation, or a lesser or greater value based on groundwater mounding analysis. See below and [[Groundwater]] for more information.
* Step 6: Adjust component depths to maintain a separation of 1.0 metre between base of the practice and seasonally high water table or top of bedrock elevation, or a lesser or greater value based on groundwater mounding analysis. See below and [[Groundwater]] for more information.