|''A<sub>i''||m<sup>2</sup>||Catchment impervious area
|''A<sub>i''||m<sup>2</sup>||Catchment impervious area
|-
|-
−
|''d<sub>r</sub>''||m||Storage reservoir depth
+
|''d<sub>r</sub>''||m||Water storage reservoir depth. For practices without an underdrain (i.e. full infiltration design), d<sub>r</sub> is the total depth of the practice (i.e. includes surface ponding and filter media depths). For practices with an underdrain (i.e. partial infiltration design), d<sub>r</sub> is the depth below the invert of the underdrain perforated pipe outlet.
|-
|-
−
|''d<sub>T</sub>''||m||Total depth of the practice
+
|''A<sub>p</sub> is the''||m<sup>2</sup>||Permeable footprint area of the practice. For practices where runoff is directed to a surface ponding area, A<sub>p</sub> is the surface ponding area. For practices where runoff is directed to a subsurface water storage reservoir, A<sub>p</sub> is the footprint area of the storage reservoir, A<sub>r</sub>
−
|-
−
|''A<sub>p''||m<sup>2</sup>||Permeable footprint area of the practice
−
|-
−
|''A<sub>r''||m<sup>2</sup>||Storage reservoir footprint area of the practice