Changes

* Design storm duration, D (h)

* Design storm duration, D (h)

* Infiltration volume target for the design storm event, V_i (m³), based on average annual water budgets for the catchment for pre- and post-development scenarios and equal to the infiltration volume deficit (pre-development minus post-development annual infiltration)

* Infiltration volume target for the design storm event, V_i (m³), based on average annual water budgets for the catchment for pre- and post-development scenarios and equal to the infiltration volume deficit (pre-development minus post-development annual infiltration)

* Drainage time t (h), time required to fully drain the active water storage components of the practice (i.e surface ponding and infiltration water storage depths), based on local criteria or long term average inter-event period for the location

* Drainage time, t (h), time required to fully drain the active water storage components of the practice (i.e surface ponding and infiltration water storage depths), based on local criteria or long term average inter-event period for the location

* Field measured infiltration rate of the underlying native soil, f (mm/h), median of measurements or based on interpolation from median grain-size distribution results

* Field measured infiltration rate of the underlying native soil, f (mm/h), median of 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, f divided by a safety factor, z

* Design infiltration rate of the underlying native soil, f' (mm/h), median field measured value, f divided by a safety factor, z

* Proposed surface grade elevation at the practice location (metres above sea level, masl)

* Proposed surface grade elevation at the practice location (metres above sea level, masl)

* Elevation of the seasonally high water table or bedrock surface (metres above sea level, masl), below the practice location

* Elevation of the seasonally high water table or bedrock surface (metres above sea level, masl), below the practice location

* Effective porosity of any void-producing structure system (e.g. soil cells, chambers and associated aggregate) included in the storage reservoir, n'

* Effective porosity of the storage reservoir fill material(s), including any void-producing structure system (e.g. soil cells, chambers and associated aggregate) included, n_r'

* 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 surface ponding area, or directly to storage reservoir)

* How runoff will be delivered to the practice (i.e. to surface ponding area, or directly to storage reservoir)

{{Plainlist|1=Where:

{{Plainlist|1=Where:

*''f''' = Design infiltration rate (mm/h), and

*''f''' = Design infiltration rate (mm/h), and

*48 = Maximum permissible drainage time for ponded water (h)}}

*48 = Maximum permissible drainage time for surface ponded water (h)}}

Note that in designs without underdrains, when filled to their maximum storage capacity, drainage of ponded water is limited by the infiltration rate at the base of the practice.<br>

Note that conceptually, in designs without underdrains, when filled to their maximum storage capacity, drainage of ponded water is limited by the infiltration rate at the base of the practice.<br>

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For practices with underdrains see recommended maximum surface ponding depth for each filter media blend in the table above.<br>

For practices with underdrains see recommended maximum surface ponding depth for each filter media blend in the table above.<br>

* Step 3: Select a design surface ponding depth, d_p' (m) to begin sizing with:<br>

* Step 3: Select a design surface ponding depth, d_p' (m) to begin sizing with:<br>

For practices with soft (i.e. landscaped) edges and bowl-shaped ponding areas calculate the mean surface ponding depth:

For practices with soft (i.e. landscaped) edges and bowl-shaped ponding areas calculate the mean surface ponding depth:

<math>d_{p}'=d_{p, max}\times 1/2</math>

<math>d_{p}'=d_{p, max}\times 0.5</math>

{{Plainlist|1=Where:

{{Plainlist|1=Where:

*d_{p, max} = maximum surface ponding depth (m)}}<br>

*d_{p, max} = maximum surface ponding depth (m)}}<br>

==Determine the infiltration water storage depth of the practice==

==Determine the infiltration water storage depth of the practice==

* Step 4: Calculate the infiltration water storage depth of the practice, d_i which is the depth of water stored in the practice that can drain by infiltration alone.<br>

* Step 4: Calculate the infiltration water storage depth of the practice, d_i which is the depth of water stored by the practice that can drain by infiltration alone.<br>

For practices without an underdrain, components contributing to infiltration water storage include the surface ponding, mulch and filter media depths (i.e. total depth of the practice).  The infiltration water storage depth of the practice can be calculated as:

For practices without an underdrain, components contributing to infiltration water storage include the surface ponding, mulch and filter media depths (i.e. total depth of the practice).  The infiltration water storage depth of the practice can be calculated as:

<math>d_{i}=d_{p}'+ (d_{m}\times n_{m}) + (d_{f}\times n_{f})</math>

<math>d_{i}=d_{p}'+ (d_{m}\times n_{m}) + (d_{f}\times n_{f})</math>

*d_f = Depth of filter media (m)

*d_f = Depth of filter media (m)

*n_f = Porosity of filter media}}<br>

*n_f = Porosity of filter media}}<br>

For practices with the underdrain perforated pipe elevated off the bottom of the storage reservoir, infiltration water storage is provided by the depth of storage reservoir below the invert of the underdrain perforated pipe, and only the portion that can reliably drain by infiltration within the specified drainage time, t.  So the infiltration water storage depth of the practice can be calculated as:

For practices with the underdrain perforated pipe elevated off the bottom of the storage reservoir, infiltration water storage is provided by the storage reservoir (depth below the invert of the underdrain perforated pipe), and only the portion that can reliably drain by infiltration within the specified inter-event drainage time, t.  So the infiltration water storage depth of the practice can be calculated as:

<math>d_{i}= f' t </math>

<math>d_{i}= f' t </math>

{{Plainlist|1=Where:

{{Plainlist|1=Where:

*D = Design storm duration (h)}}<br>

*D = Design storm duration (h)}}<br>

* Step 6: Compare required surface area of the practice to available space.<br>

* Step 6: Compare required surface area of the practice to available space.<br>

To decrease A_p, consider increasing ponding depth if feasible and would not create a safety hazard (recommended maximum of 0.45 m), or decreasing the catchment area.

To decrease A_p, consider increasing ponding depth if feasible and would not create a safety hazard (recommended maximum of 0.45 m), using Darcy 3D drainage equation or tool (see below) to optimize the infiltration water storage depth, assuming both vertical and horizontal drainage, or decreasing the catchment area.

* Step 7:  Calculate catchment impervious area to practice permeable (footprint) area ratio, R, also referred to as I/P ratio:

* Step 7:  Calculate catchment impervious area to practice permeable (footprint) area ratio, R, also referred to as I/P ratio:

<math>R=A_{i}/A_{p}</math><br>

<math>R=A_{i}/A_{p}</math><br>

Adjust d_p, d_i, A_p or A_i to keep R between 5 and 20.

Adjust d_p, d_i, A_p or A_i to keep R between 5 and 20, and solve the applicable sizing equation from above to determine the required dimensions of the practice.

==Determine the required surface area of the storage reservoir==

==Determine the required surface area of the storage reservoir==

*f' = Design infiltration rate of the underlying native soil (m/h)

*f' = Design infiltration rate of the underlying native soil (m/h)

*D= Duration of design storm (h)<br>

*D= Duration of design storm (h)<br>

If A_r is greater than A_p, use the value for A_r as the required footprint area of the practice.  

For practices where inflow is directed to a surface ponding area, if A_r is greater than A_p, use the value for A_r as the required footprint area of the practice, A_p.  

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*Step 9: Calculate the required storage reservoir depth, d_r (m):

*Step 9: Calculate the required storage reservoir depth, d_r (m):

*d_i' = Design infiltration water storage depth (m)

*d_i' = Design infiltration water storage depth (m)

*n_r' = Effective porosity of the storage reservoir fill material(s).<br>

*n_r' = Effective porosity of the storage reservoir fill material(s).<br>

If the storage reservoir would need to be greater than 0.6 metres deep if filled with clear stone aggregate with porosity (n) of 0.4, consider installing a void-producing structure embedded in clear stone aggregate instead, which will provide a greater effective porosity (n'), allow for a shallower storage reservoir depth, and save aggregate.

To minimize the total depth of the practice, d_T, and save aggregate, consider installing void-producing structures, embedded in clear stone aggregate, in the storage reservoir instead of just aggregate, which will provide a greater effective porosity (n').

==Calculate the total depth of the practice, d_T==

==Calculate the total depth of the practice, d_T==

* Step 10: Determine what the planting needs are and assign an appropriate depth of filter media, using the table above.  

* Step 10: Determine what the planting needs are and assign an appropriate depth of filter media, using the table above.  

* Step 11: Select an underdrain perforated pipe diameter (typically 100 or 200 mm), assign this as an 'embedded' depth equal to the pipe diameter. The perforated pipe depth can be made part of the active infiltration water storage of the practice when a riser (standpipe and 90 degree coupling) are used to design the underdrain.   

* Step 11: Select an underdrain perforated pipe diameter (typically 100 or 200 mm), assign this as an 'embedded' depth equal to the pipe diameter. The perforated pipe depth can be made part of the infiltration water storage of the practice when a riser (standpipe and 90 degree coupling) are used to design the underdrain.   

* Step 12: Sum total depth of bioretention components, and compare to available space (i.e. depth) between the elevations of the proposed surface grade and one (1) metre above the seasonally high water table or top of bedrock in the practice location.  

* Step 12: Sum total depth of bioretention components, and compare to available space (i.e. depth) between the elevations of the proposed surface grade and one (1) metre above the seasonally high water table or top of bedrock in the practice location.  

* Step 13: Adjust component depths to maintain a separation of one (1) metre between the base of the practice and the 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.<br>

* Step 13: Adjust component depths to maintain a separation of one (1) metre between the base of the practice and the 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.<br>

*To estimate the time (''t'') to fully drain the facility:

*To estimate the time (''t'') to fully drain the facility:

   

   

<math>t=\frac{nA_{p}}{f'x}ln\left [\frac{\left (d_{T}+ \frac{A_{p}}{x} \right )}{\left(\frac{A_{p}}{x}\right)}\right]</math>

<math>t=\frac{nA_{p}}{f'x}\times ln\left [\frac{\left (d_{T}+ \frac{A_{p}}{x} \right )}{\left(\frac{A_{p}}{x}\right)}\right]</math>

{{Plainlist|1=Where:

{{Plainlist|1=Where: