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→Drainage time (3D)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.
t = [n<sub>r</sub>' * A<sub>p</sub>/f'*x] * ln[(d<sub>r</sub> + (A<sub>p</sub>/x)/A<sub>p</sub>/x]
t = [n<sub>r</sub>' * A<sub>p</sub>/f'*x] * ln[(d<sub>r</sub> + (A<sub>p</sub>/x)/A<sub>p</sub>/x]
{{Plainlist|1=Where:
{{Plainlist|1=Where:
*''n'' is the porosity of the filter media,
*''n<sub>r</sub>''' is the effective porosity of the storage reservoir fill material(s),
*''A<sub>p</sub>'' is the area of the practice (m<sup>2</sup>),
*''A<sub>p</sub>'' is the area of the practice (m<sup>2</sup>),
*''f''' is the design infiltration rate (mm/hr),
*''f''' is the design infiltration rate of the native soil (mm/h),
*''x'' is the perimeter of the practice (m), and
*''x'' is the perimeter of the practice (m), and
*''d<sub>T</sub>'' is the total depth of the practice, including the surface ponding depth (m).}}
*''d<sub>r</sub>'' is the depth of the storage reservoir (m).}}
===Groundwater mounding===
===Groundwater mounding===