Changes

[[File:Sizing Bioretention.jpg|thumb|The vertical storage zones in a bioretention cell include: ponding, mulch, filter media, choker layer, embedded pipe diameter depth and the storage reservoir.]]  

[[File:Sizing Bioretention.jpg|thumb|The vertical storage zones in a bioretention cell include: ponding, mulch, filter media, choker layer, embedded pipe diameter depth and the storage reservoir.]]  

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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 and the depth of the 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 storage reservoir beneath the optional underdrain pipe. The table below describes some recommended values to use to begin the design process.   

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{| class="wikitable"

* Step 16. 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 time assuming one dimensional (1D) drainage===

This spreadsheet compares drainage in a single dimension under zero head conditions, mean head conditions and falling head conditions. It provides a more conservative measurement of the drainage time for the purposes of groundwater mounding (where a shorter drainage time causes a greater impact).  

This spreadsheet allows calculation of drainage time assuming one dimensional drainage under zero head conditions, mean head conditions and falling head conditions. It provides a conservative estimate of drainage time for the purposes of groundwater mounding analysis, where shorter drainage times cause a greater impact.  

{{Clickable button|[[Media:Darcy drainage.xlsx|Download drainage time calculator(.xlsx)]]}}

{{Clickable button|[[Media:Darcy drainage.xlsx|Download drainage time calculator(.xlsx)]]}}

===Drainage time (3D)<ref>Woods Ballard, B., S. Wilson, H. Udale-Clarke, S. Illman, T. Scott, R. Ahsley, and R. Kellagher. 2016. The SuDS Manual. 5th ed. CIRIA, London.</ref>===

===Calculating infiltration practice drainage time assuming three dimensional (3D) drainage<ref>Woods Ballard, B., S. Wilson, H. Udale-Clarke, S. Illman, T. Scott, R. Ahsley, and R. Kellagher. 2016. The SuDS Manual. 5th ed. CIRIA, London.</ref>===

[[file:Hydraulic radius.png|thumb|Two practice areas of 9 m².<br> x = 12 m (left), x = 20 m (right)]]

[[file:Hydraulic radius.png|thumb|Two practice areas of 9 m².<br> x = 12 m (left), x = 20 m (right)]]

In some situations, it may be desirable to reduce the size of the bioretention required, by accounting for rapid drainage.  

In some situations, it may be desirable to optimize the size of the bioretention practice, by accounting for drainage in three dimensions rather than one.  

Typically, this is only worth exploring over sandy textured native subsoils with rapid infiltration.  

Typically, this is only worth exploring over sandy textured native subsoils with rapid infiltration.  

The drainage time calculator noted above can be used to calculate drainage time assuming three dimensional drainage as well.

The drainage time calculator noted above can be used to calculate drainage time assuming both one and three dimensional drainage and allows for comparison between the estimates.

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

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