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→Determine the required surface area of the storage reservoir
*d<sub>i</sub> = Infiltration water storage depth of the practice (m), see equations above to calculate for with and without underdrain designs.
*d<sub>i</sub> = Infiltration water storage depth of the practice (m), see equations above to calculate for with and without underdrain designs.
*f' = Design infiltration rate of the underlying native soil (m/h)
*f' = Design infiltration rate of the underlying native soil (m/h)
*D= Duration of design storm (h)<br>
*D= Duration of design storm (h)}}<br>
For practices where inflow is directed to a surface ponding area, if A<sub>r</sub> is greater than A<sub>p</sub>, use the value for A<sub>r</sub> as the required footprint area of the practice, A<sub>p</sub>.
For practices where inflow is directed to a surface ponding area, if A<sub>r</sub> is greater than A<sub>p</sub>, use the value for A<sub>r</sub> as the required footprint area of the practice, A<sub>p</sub>.
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{{Plainlist|1= Where:
{{Plainlist|1= Where:
*d<sub>i</sub>' = Design infiltration water storage depth (m)
*d<sub>i</sub>' = Design infiltration water storage depth (m)
*n<sub>r</sub>' = Effective porosity of the storage reservoir fill material(s).<br>
*n<sub>r</sub>' = Effective porosity of the storage reservoir fill material(s).}}<br>
To minimize the total depth of the practice, d<sub>T</sub>, and save aggregate, consider installing void-forming structures (e.g. Permavoid, D-Raintank, low profile stormwater chamber, large diameter perforated pipes etc.) embedded in clear stone aggregate in the storage reservoir instead of aggregate alone, which will provide a greater effective porosity (n').
To minimize the total depth of the practice, d<sub>T</sub>, and save aggregate, consider installing void-forming structures (e.g. Permavoid, D-Raintank, low profile stormwater chamber, large diameter perforated pipes etc.) embedded in clear stone aggregate in the storage reservoir instead of aggregate alone, which will provide a greater effective porosity (n').