Changes

To boost drainage performance on fine-textured, low permeability soils, consider designing storage reservoirs even deeper than those calculated using the above approach, that many not fully drain between storm events, which increases hydraulic head and infiltration rate at the base of the practice. See [[Low permeability soils]] for more information.

To boost drainage performance on fine-textured, low permeability soils, consider designing storage reservoirs even deeper than those calculated using the above approach, that many not fully drain between storm events, which increases hydraulic head and infiltration rate at the base of the practice. See [[Low permeability soils]] for more information.

==Determine the required surface area of the practice==

==Determine the required surface area of the practice==

* Step 9: Calculate the surface area of the practice (A_p) needed to capture the volume of runoff produced from the catchment from the design storm event<br>

* Step 5: Calculate the surface area of the practice (A_p) needed to capture the volume of runoff produced from the catchment from the design storm event<br>

For practices where flow is delivered to a surface ponding area:

For practices where flow is delivered to a surface ponding area:

<math>A_{p}=i\times D\times A_{i}/[d_{p}' + (f_{f, min} \times D)]</math>

<math>A_{p}=i\times D\times A_{i}/[d_{p}' + (f_{f, min} \times D)]</math>

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

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

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

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

* Step 10: 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, or decreasing catchment impervious area.

To decrease A_p, consider increasing ponding depth if feasible and would not create a safety hazard, or decreasing catchment impervious area.

* Step 11:  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 either A_i or A_p to keep R between 5 and 20.

Adjust either A_i or A_p to keep R between 5 and 20.

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

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

* Step 12: Calculate the surface area of the storage reservoir, A_r (m²) needed to capture the infiltration volume target for the design storm event: <math>A_{r}=V_{i}/[d_{i}+(f'\times D)]</math>

* Step 8: Calculate the surface area of the storage reservoir, A_r (m²) needed to capture the infiltration volume target for the design storm event: <math>A_{r}=V_{i}/[d_{i}+(f'\times D)]</math>

{{Plainlist|1=Where:

{{Plainlist|1=Where:

*V_i = Infiltration volume target for the design storm event (m³), based on average annual water budgets for pre- and post-development scenarios, and the target of maintaining pre-development infiltration volume.

*V_i = Infiltration volume target for the design storm event (m³), based on average annual water budgets for pre- and post-development scenarios, and the target of maintaining pre-development infiltration volume.

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

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

<br>

<br>

*Step 13: Calculate the required storage reservoir depth, d_r (m):

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

<math>d_{r}=d_{i}\times 1/n_{r}'</math>

<math>d_{r}=d_{i}\times 1/n_{r}'</math>

{{Plainlist|1=Where:

{{Plainlist|1=Where:

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

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

* Step 14: 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 15: 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 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 active storage of the practice when a riser (standpipe and 90 degree coupling) are used to design the underdrain.   

* Step 16: Sum total depth of bioretention components, and compare to available space (i.e. depth) between the proposed surface grade and one (1) metre above the seasonally high water table or top of bedrock elevation in the practice location.  

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

* Step 17: 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>

For practices without an underdrain in locations constrained in the vertical dimension, consider decreasing filter media depth (and supported plant types) and/or catchment impervious area.<br>

For practices without an underdrain in locations constrained in the vertical dimension, consider decreasing filter media depth (and supported plant types) and/or catchment impervious area.<br>

For practices with an underdrain in locations constrained in the vertical dimension, consider installing the perforated pipe on the bottom of the storage reservoir and including a riser (saves the depth of aggregate needed to embed the pipe), and/or decreasing filter media depth (and supported plant types), ponding depth and/or catchment impervious area.

For practices with an underdrain in locations constrained in the vertical dimension, consider installing the perforated pipe on the bottom of the storage reservoir and including a riser (saves the depth of aggregate needed to embed the pipe), and/or decreasing filter media depth (and supported plant types), ponding depth and/or catchment impervious area.

==Calculate peak flow rates==  

==Calculate peak flow rates==  

* Step 18. Calculate the peak [[flow through perforated pipe|flow rate through the perforated pipe]],  

* Step 14. Calculate the peak [[flow through perforated pipe|flow rate through the perforated pipe]],  

* Step 19. Calculate the peak [[flow through media|flow rate through the filter media]],  

* Step 15. Calculate the peak [[flow through media|flow rate through the filter media]],  

* Step 20. Determine if downstream [[flow control]] is required to achieve hydrologic objectives.

* Step 16. Determine if downstream [[flow control]] is required to achieve hydrologic objectives.

===Calculating infiltration practice drainage in 1 dimension===

===Calculating infiltration practice drainage in 1 dimension===