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+==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.
−
! 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
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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==