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→Determine the required surface area of the practice
* Step 5: Calculate the surface area of the practice (A<sub>p</sub>) needed to capture the volume of runoff produced from the catchment by the design storm event.<br>
* Step 5: Calculate the surface area of the practice (A<sub>p</sub>) needed to capture the volume of runoff produced from the catchment by the design storm event.<br>
For practices where flow is delivered to a surface ponding area:
For practices where flow is delivered to a surface ponding area:
<math>A_{p}=i\times D\times A_{i}/[d_{p}' + (f_{f, min} \times D)]</math>
<math>A_{p}=i\times D\times A_{i}/[d_{p}' + (K_{f} \times D)]</math>
{{Plainlist|1=Where:
{{Plainlist|1=Where:
*i = Design storm intensity (m/h)
*i = Design storm intensity (m/h)
*A<sub>i</sub> = Catchment impervious area (m<sup>2</sup>)
*A<sub>i</sub> = Catchment impervious area (m<sup>2</sup>)
*d<sub>p</sub>' = Design surface ponding depth (m)
*d<sub>p</sub>' = Design surface ponding depth (m)
*f<sub>f, min</sub> = minimum acceptable infiltration rate (i.e. saturated hydraulic conductivity) of the filter media (m/h), see [[Bioretention: Filter media|Filter media]] for guidance}}<br>
*K<sub>f</sub> = minimum acceptable saturated hydraulic conductivity of the filter media (m/h), see [[Bioretention: Filter media|Filter media]] for guidance}}<br>
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For practices where flow is delivered directly to the storage reservoir:
For practices where flow is delivered directly to the storage reservoir: