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Line 86: ==Step 3, depth of bowl,''d<sub>b</sub>''==[[File:Sizing bio2.png|thumb|The duration of surface ponding is usually determined by the emptying of the facility below.]] <poem>The 'bowl' area is simply the depressed elevation of the surface compared to the surrounding areas; a space to permit temporary ponding. The depth of the bowl would not typically exceed 0.5 m due to safety concerns. Some jurisdictions or particular sites may demand a lower maximum depth of ponding. It is worth bearing in mind that in most cases this ponded water will only occur once or twice per year.The ponded water within the bowl should drain within 48 hrs. This addresses public concerns about [[mosquitoes]] and reduces the probability of losing vegetation due to saturated growing conditions. The drainage of the bowl is not usually constrained by the surface infiltration (filter media should drain > 25 mm/hr). The infiltration of water from the bowl is determined by the drainage of the filter media and reservoir into the soils.
no edit summary
! Recommended depth (with underdrain pipe)
! Recommended depth (with underdrain pipe)
! Recommended depth (no underdrain pipe)
! Recommended depth (no underdrain pipe)
! Typical void ratio (''V<sub>r</sub>'')
! Typical void ratio (''V<sub>R</sub>'')
|-
|-
| Ponding depth
| Ponding depth
Note that narrow, linear bioretention features drain faster than round or blocky footprint geometries.
Note that narrow, linear bioretention features drain faster than round or blocky footprint geometries.
*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'').
*To estimate the time (''t'') to fully drain the facility:
To estimate the time (''t'') to fully drain the facility:
:<math>t=\frac{V_{R}A_{p}}{f'P}ln\left [ \frac{\left (d+ \frac{A_{p}}{P} \right )}{\left(\frac{A_{p}}{P}\right)}\right]</math>
:<math>t=\frac{V_{R}A_{p}}{f'P}ln\left [ \frac{\left (d+ \frac{A_{p}}{P} \right )}{\left(\frac{A_{p}}{P}\right)}\right]</math>
</poem>
{{Plainlist|1=Where:
*''V<sub>R</sub>'' is the void ratio of the media,
*''A<sub>p</sub>'' is the area of the practice (m<sup>2</sup>),
*''f''' is the design infiltration rate (mm/hr), and
.}}
==Groundwater mounding==
==Groundwater mounding==