Line 55: |
Line 55: |
| * 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) |
Line 64: |
Line 64: |
| * 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), |
Line 83: |
Line 109: |
| *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. |