Changes

Before beginning the sizing calculations most of the following parameters must be known or estimated.  

The exceptions are the depth (''d_T'') and practice permeable (footprint) area (''A_p''), as only one of these is required to find the other.  

Note that some of these parameters are limited:

Before beginning the sizing calculations certain parameters must be known or estimated. See [[Bioretention: Sizing]] for parameter descriptions and conceptual diagram illustrating key components of bioretention practices. Note that some of these parameters are limited:

#The ''maximum'' total depth will be limited by construction practices i.e. not usually > 2 m.

#The ''maximum'' total depth will be limited by construction practices i.e. not usually > 2 m.

#The ''maximum'' total depth may be limited by the [[Infiltration| conditions underground]] e.g. the groundwater or underlying geology/infrastructure.

#The ''maximum'' total depth may be limited by the [[Infiltration| conditions underground]] e.g. the groundwater or underlying geology/infrastructure.

*''i'' = Intensity of design storm (mm/h)

*''i'' = Intensity of design storm (mm/h)

*''f''' = [[design infiltration rate]] (m/h)

*''f''' = [[design infiltration rate]] (m/h)

*''n''' = Effective porosity of the fill materials within the active storage component(s) of practice, depth-weighted mean

*''n''' = Effective porosity of the fill material in the storage reservoir of the practice

*''d_r'' = Storage reservoir depth, based on depth available between the elevation of the invert of the underdrain perforated pipe and one (1) metre above the seasonally high water table or top of bedrock  (m) or other value determined to be suitable through groundwater mounding analysis.}}<br>

*''d_r'' = Storage reservoir depth, based on depth available between the elevation of the invert of the underdrain perforated pipe and one (1) metre above the seasonally high water table or top of bedrock  (m) or other value determined to be suitable through groundwater mounding analysis.}}<br>

If R is greater than 20, consider decreasing catchment impervious area (A_i) by draining less area to the practice.

If R is greater than 20, consider decreasing catchment impervious area (A_i) by draining less area to the practice.

==Size a bioretention cell with no underdrain for constrained ground area==

==Size a bioretention cell where drainage area and practice area are fixed==

If the land area is limited, determine the I/P ratio, which is the ratio of catchment impervious area (A_i) to practice pervious footprint area (A_p):

If the land area is limited, determine the I/P ratio, which is the ratio of catchment impervious area (A_i) to practice pervious footprint area (A_p):

:<math>R=\frac{A_{i}}{A_{p}}</math>

:<math>R=\frac{A_{i}}{A_{p}}</math>

*''A_i'' = Catchment impervious area in m²}}

*''A_i'' = Catchment impervious area in m²}}

Then calculate the required depth (''d_T''), as:

Then calculate the required storage reservoir depth (''d_r''), as:

<math>d_{T}=\frac{D \left[ (R\times i)-f'\right]}{n'}</math>

<math>d_{r}=\frac{D \left[ (R\times i)-f'\right]}{n'}</math>

{{Plainlist|1=Where:

{{Plainlist|1=Where:

*''i'' = Intensity of design storm (m/h)

*''i'' = Intensity of design storm (m/h)

*''f''' = Design infiltration rate (m/h)  

*''f''' = Design infiltration rate (m/h)  

*''n''' = Effective porosity of the fill materials within the practice, depth weighted mean

*''n''' = Effective porosity of the storage reservoir fill material}}

*''d_T'' = Total depth of infiltration practice (m).}}

These equations assume that infiltration occurs primarily through the base of the facility.<br>

These equations assume that infiltration occurs primarily through the base of the facility.  

This spreadsheet tool has been set up to perform all of the infiltration practice sizing calculations shown above.<br>

 

{{Clickable button|[[Media:Infiltration Sizing 20220617 locked (1).xlsx|Download the infiltration practice sizing tool]]}}

This spreadsheet tool has been set up to perform all of the infiltration BMP sizing calculations shown above<br>

{{Clickable button|[[Media:Infiltration Sizing 20200525 locked.xlsx|Download the infiltration practice sizing tool]]}}

==Calculate drawdown time==

==Calculate drawdown time==