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To calculate the require facility area or footprint where the depth is constrained:
To calculate the require facility area or footprint where the depth is constrained:
<math>A_{p}=\frac{IiD}{V_{R}d+\left ( \frac{q}{SCF} \right )D}</math>
<math>A_{p}=\frac{IiD}{V_{R}d+\left ( \frac{q}{SCF} \right )D}</math>
{{Plainlist|1=Where:
*''D'' = Duration of design storm in hrs
*''i'' = Intensity of design storm in mm/hr
*''q'' = Infiltration rate of underlying soil in mm/hr
*''SF'' = Safety factor
*''V<sub>R</sub>'' = Void ratio (porosity), as measured (or default to 0.35 for all aggregates)*
*''R'' = Ratio of catchment area (''A<sub>c</sub>'') to BMP footprint area (A<sub>p</sub>) syn. I/P ratio.
*''A<sub>p</sub>'' = Area of the infiltration practice in m<sup>2</sup>
*''A<sub>c</sub>'' = Catchment area in m<sup>2</sup>
*''d'' = Depth of infiltration practice in m.}}
*Note: For systems that have significant storage in clear open chambers, an effective porosity value (''V<sub>R</sub><nowiki>'</nowiki>'') may be estimated for the whole installation and used in the calculations below. Effective porosity will vary according to the geometry of the storage chambers, so advice should be sought from product manufacturers. Permit applications should include the basis for ''V<sub>R</sub><nowiki>'</nowiki>'' estimates.
This spreadsheet tool has been set up to perform either of the above calculations.<br>
This spreadsheet tool has been set up to perform either of the above calculations.<br>