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This article is specific to [[bioretention]], vegetated systems that infiltrate water to the native soil. <br>
[[File:Bioretention sizing update.png|thumb|550px|The vertical storage zones in a bioretention cell include: ponding, mulch, filter media, choker layer, embedded pipe diameter depth and the internal water storage (IWS) reservoir.]]
If you are designing a planted system which does not infiltrate water, see advice on [[Planters: Sizing]].
This article is specific to [[bioretention]], vegetated systems that infiltrate water to the native soil.
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If you are designing a planted system which does not infiltrate water, see advice on [[Planters: Sizing]].<br>
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<br>
Many of the dimensions in a bioretention system can be predetermined according to the function of the component. There is greatest flexibility in the ponding depth, filter media depth and the depth of the internal water storage reservoir beneath the optional underdrain pipe. The table below describes some recommended values to use to begin the design process.
Many of the dimensions in a bioretention system can be predetermined according to the function of the component. There is greatest flexibility in the ponding depth, filter media depth and the depth of the internal water storage reservoir beneath the optional underdrain pipe. The table below describes some recommended values to use to begin the design process.
<br>
{| class="wikitable"
{| class="wikitable"
|-
|-
| 0.4 for clear stone aggregate in which the pipe is embedded
| 0.4 for clear stone aggregate in which the pipe is embedded
|-
|-
| Storage reservoir (''d<sub>r</sub>'')
| [[Bioretention: Internal water storage|Internal water storage reservoir]] (''d<sub>r</sub>'')
| See below
| See below
| See below
| See below
This spreadsheet tool has been set up to perform all of the bioretention sizing calculations shown below and allows side-by-side comparison of equation outputs for each potential design approach or constraint scenario.<br>
This spreadsheet tool has been set up to perform all of the bioretention sizing calculations shown below and allows side-by-side comparison of equation outputs for each potential design approach or constraint scenario.<br>
{{Clickable button|[[Media:Infiltration Sizing 20200525 locked.xlsx|Download the infiltration practice sizing tool]]}}
{{Clickable button|[[Media:Infiltration Sizing 20220617 locked (1).xlsx|Download the infiltration practice sizing tool]]}}
==Decide if an underdrain will be included==
==Decide if an underdrain will be included==
*K<sub>f</sub> = minimum acceptable saturated hydraulic conductivity of the filter media (m/h), see [[Bioretention: Filter media|Filter media]] for guidance}}<br>
*K<sub>f</sub> = minimum acceptable saturated hydraulic conductivity of the filter media (m/h), see [[Bioretention: Filter media|Filter media]] for guidance}}<br>
<br>
<br>
For practices where flow is delivered directly to the storage reservoir:
For practices where flow is delivered directly to a subsurface (underground) water storage reservoir:
<math>A_{p}=i\times D\times A_{i}/[d_{i} + (f' \times D)]</math>
<math>A_{p}=i\times D\times A_{i}/[d_{i} + (f' \times D)]</math>
{{Plainlist|1=Where:
{{Plainlist|1=Where:
*d<sub>i</sub> = Infiltration water storage depth (m), see above for equations for with and without underdrain designs
*d<sub>i</sub> = Infiltration water storage depth (m), see above for equations for with and without underdrain designs
*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 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>
You can use the infiltration practice sizing tool noted above to adjust d<sub>p</sub>, d<sub>i</sub>, A<sub>p</sub> or A<sub>i</sub> to find practice dimensions that provide the required storage volume and will drain within the specified drainage time, while keeping R between 5 and 20.
You can use the infiltration practice sizing tool noted above to adjust d<sub>p</sub>, d<sub>i</sub>, A<sub>p</sub> or A<sub>i</sub> to find practice dimensions that provide the required storage volume and will drain within the specified drainage time, while keeping R between 5 and 20.
==Determine the required surface area of the storage reservoir==
==Determine the required surface area of the internal water storage reservoir==
* Step 8: Calculate the surface area of the storage reservoir, A<sub>r</sub> (m<sup>2</sup>) 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<sub>r</sub> (m<sup>2</sup>) 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: