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→Drainage time (3D)
===Drainage time (3D)===
===Drainage time (3D)===
[[file:Hydraulic radius.png|thumb|Two practice areas of 9 m<sup>2</sup>.<br> P = 12 m (left), P = 20 m (right)]]
[[file:Hydraulic radius.png|thumb|Two practice areas of 9 m<sup>2</sup>.<br> P = 12 m (left), P = 20 m (right)]]
In some situations, it may be possible to reduce the size of the biortention required, by accounting for rapid drainage. Typically, this is only worth exploring over sandy soils with rapid infiltration.
In some situations, it may be possible to reduce the size of the bioretention required, by accounting for rapid drainage. Typically, this is only worth exploring over sandy soils with rapid infiltration.
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'').