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==Size a bioretention cell for constrained depth==
==Size a bioretention cell for constrained depth==
If there is a constraint to the depth (''d<sub>T</sub>'', m) of the practice, calculate the required footprint area (''A<sub>p</sub>'', m<sup>2</sup>), as:
If there is a constraint to the depth (''d<sub>T</sub>'', m) of the practice, calculate the required footprint area (''A<sub>p</sub>'', m<sup>2</sup>), as:
<math>A_{p}=\frac{A_c\times i\times D}{(V_{R}\times d_{T})+(f'\times D)}</math>
<math>A_{p}=\frac{A_c\times i\times D}{(n\times d_{T})+(f'\times D)}</math>
{{Plainlist|1=Where:
{{Plainlist|1=Where:
*''A<sub>p</sub>'' = Area of the infiltration practice in m<sup>2</sup>
*''A<sub>p</sub>'' = Area of the infiltration practice in m<sup>2</sup>
*''i'' = Intensity of design storm in mm/hr
*''i'' = Intensity of design storm in mm/hr
*''f''' = [[design infiltration rate]] in mm/hr
*''f''' = [[design infiltration rate]] in mm/hr
*''V<sub>R</sub>'' = Mean void ratio of the fill within the practice
*''n'' = Mean porosity of the fill within the practice
*''d<sub>T</sub>'' = Total depth of the infiltration practice in m.}}
*''d<sub>T</sub>'' = Total depth of the infiltration practice in m.}}
Then calculate the required depth (''d<sub>T</sub>''), as:
Then calculate the required depth (''d<sub>T</sub>''), as:
<math>d_{T}=\frac{D \left[ (R\times i)-f'\right]}{V_{R}}</math>
<math>d_{T}=\frac{D \left[ (R\times i)-f'\right]}{n}</math>
{{Plainlist|1=Where:
{{Plainlist|1=Where:
*''i'' = Intensity of design storm in mm/hr
*''i'' = Intensity of design storm in mm/hr
*''f''' = Design infiltration rate in mm/hr
*''f''' = Design infiltration rate in mm/hr
*''V<sub>R</sub>'' = Void ratio
*''n'' = Porosity
*''d<sub>T</sub>'' = Depth of infiltration practice in m.}}
*''d<sub>T</sub>'' = Depth of infiltration practice in m.}}
The following equations assume that infiltration occurs primarily through the base of the facility.
The following equations assume that infiltration occurs primarily through the base of the facility.
*Begin the drainage time calculation by dividing the area of the practice (''A<sub>p</sub>'') by the perimeter (''P'').
*Begin the drainage time calculation by dividing the area of the practice (''A<sub>p</sub>'') by the perimeter (''P'').
*Use the following equation to estimate the time (''t'') to fully drain the facility:
*Use the following equation to estimate the time (''t'') to fully drain the facility:
:<math>t=\frac{V_{R}A_{p}}{f'P}ln\left [ \frac{\left (d_{T}+ \frac{A_{p}}{P} \right )}{\left(\frac{A_{p}}{P}\right)}\right]</math>
:<math>t=\frac{nA_{p}}{f'P}ln\left [ \frac{\left (d_{T}+ \frac{A_{p}}{P} \right )}{\left(\frac{A_{p}}{P}\right)}\right]</math>
{{Plainlist|1=Where:
{{Plainlist|1=Where:
*''V<sub>R</sub>'' is the void ratio of the media,
*''n'' is the porosity of the media,
*''A<sub>p</sub>'' is the area of the practice (m<sup>2</sup>),
*''A<sub>p</sub>'' is the area of the practice (m<sup>2</sup>),
*''f''' is the design infiltration rate (mm/hr),
*''f''' is the design infiltration rate (mm/hr),