Changes

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* 0.7 for wood based

* 0.7 for wood based

* 0.4 for aggregate

* 0.4 for [[stone]]

|-

|-

| [[Bioretention: Filter media|filter media]] (''d_m'')

| [[Bioretention: Filter media|filter media]] (''d_m'')

* 600 mm to support flowering [[perennials]] and decorative [[grasses]]

* 600 mm to support flowering [[perennials]] and decorative [[grasses]]

* 1000 mm to support [[trees]]

* 1000 mm to support [[trees]]

| 0.3

*[[Bioretention media storage| 0.4]] for sandy mix

|-

|-

| [[choker layer|Choker course]]

| [[choker layer|Choker course]]

*Step 2: Select an underdrain 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.   

*Step 2: Select an underdrain 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.   

*Step 3: Calculate the maximum possible storage reservoir depth beneath the pipe (''d_{s, max}'', mm):

*Step 3: Calculate the maximum possible storage reservoir depth beneath the pipe (''d_{s, max}'', mm):

<math>d_{s, max}=\frac{f'\times t}{0.4}</math>

<math>d_{s, max}=f'\times t</math>

{{Plainlist|1=Where:

{{Plainlist|1=Where:

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

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

*''t'' = [[Drainage time]] (hrs), e.g. 96 hours, check local regulations for drainage time requirements.

*''t'' = [[Drainage time]] (hrs). Check local regulations for drainage time requirements.}}

*''0.4'' = Void ratio of [[reservoir gravel|clear stone]]}}

===Additional step for system without underdrain===

===Additional step for system without underdrain===

* Step 4: Determine maximum permissible ponding depth (''d_{p, max}''):

* Step 4: Determine maximum permissible ponding depth (''d_{p, max}''):

<math>d_{p, max}=\frac{f'\times48}{0.4}</math>

<math>d_{p, max}=f'\times48</math>

{{Plainlist|1=Where:

{{Plainlist|1=Where:

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

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

*48 = Drainage time of the ponding (hrs)

*48 = Drainage time of the ponding (hrs)

*0.4 = Void ratio of [[reservoir gravel|clear stone]] *Note that conceptually the drainage of the ponded area is limited by ex-filtration at the base of the practice.}}

*Note that conceptually the drainage of the ponded area is limited by ex-filtration at the base of the practice.}}

* Step 5: Sum total depth of bioretention, and compare to available space above water table and bedrock. Adjust if necessary.

* Step 5: Sum total depth of bioretention, and compare to available space above water table and bedrock. Adjust if necessary.

* Step 6: Multiply the depth of each separate component by the void ratio and then sum the total to find the 1 dimensional storage (in mm).

* Step 6: Multiply the depth of each separate component by the void ratio and then sum the total to find the 1 dimensional storage (in mm).

* Step 7: Calculate the required total storage (S_T, m³):

* Step 7: Calculate the required total storage (S_T, m³):

<math>S_{T}=RVC_T\times A_c\times C\times 0.1</math>

<math>S_{T}=RVC_T\times A_c\times 10</math>

{{Plainlist|1=Where:

{{Plainlist|1=Where:

*''RVC_T'' is the Runoff volume control target (mm),

*''RVC_T'' is the Runoff volume control target (mm),

*''A_c'' is the catchment area (Ha),

*''A_c'' is the catchment area (Ha), and

*''C'' is the runoff coefficient of the catchment area, and

* 10 is the units correction between m³ and mm.Ha.}}

* 0.1 is the units correction between m³ and mm.Ha.}}

* Step 8. Divide required storage (m³) by the 1 dimensional storage (in m) to find the required footprint area (''A_p'') for the bioretention in m².  

* Step 8. Divide required storage (m³) by the 1 dimensional storage (in m) to find the required footprint area (''A_p'') for the bioretention in m².  

* Step 9. Calculate the peak [[flow through perforated pipe|flow rate through the perforated pipe]],  

* Step 9. Calculate the peak [[flow through perforated pipe|flow rate through the perforated pipe]],  

Typically, this is only worth exploring over sandy soils with rapid infiltration.  

Typically, this is only worth exploring over sandy soils with rapid infiltration.  

Note that narrow, linear bioretention features ([[bioswales]]) drain faster than round or blocky footprint geometries.  

Note that narrow, linear bioretention features (or [[bioswales]]) drain faster than round or blocky footprint geometries.  

*Begin the drainage time calculation by dividing the area of the practice (''A_p'') by the perimeter (''P'').

*Begin the drainage time calculation by dividing the area of the practice (''A_p'') by the perimeter (''P'').