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Notation

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;LA<sub>c</sub> :Length, e.g. Area of a reachthe catchment, channel or swale whole contributing drainage area (usually in m<sup>2</sup>).
;mA<sub>i</sub> :run Area of side slopes in channel cross sections impervious cover within the catchment (length, but usually expressed as a ratio in relation to rise. e.g. where side side slopes = 1:3.5, m = 3<sup>2</sup>).5)
;qA<sub>p</sub> :infiltration rate in Area of the practice e.g. footprint area of a bioretention cell (length per time, usually mmin m<sup>2</hr) (before or after application of safety factor?sup>)
;R<sub>a</sub> D :Existing rise Duration of swale gradient the design storm event (lengthin units of time, usually mhrs)
;Rd<sub>bp</sub> :Rise Surface ponding depth of compensation gradient for an enhanced swale infiltration practice (unit of length, usually mmm or cm)
;SCFd<sub>m</sub> :Safety correction factor Filter media depth of a bioretention, stormwater planter or soil cell practice (dimensionlessunit of length, usually mm or cm)
;d<sub>s</sub> :Storage reservoir depth of an infiltration practice (unit of length, usually mm or cm) ;d<sub>T</sub> :Total depth of an infiltration practice (unit of length, usually cm or m) ;f :Infiltration rate, measured (usually mm/hr) ;f':Design infiltration rate (length per time, usually mm/hr) after application of safety correction factor (SCF) ;h :Height (units of length) ;i :Intensity of the design storm event (in units of depth/time, usually mm/hr) ;i :Thornthwaite monthly heat index (-) ;I :Thornthwaite annual heat index (-) ;L :Length, e.g. of a reach, channel or swale (usually in m) ;m :Run of side slopes in channel cross sections (length, but usually expressed as a ratio in relation to rise. e.g. side slopes = 1:3, so m = 3) ;n :Porosity, applies to aggregate and other void-forming materials, filter media and native soils (unit is vol/vol, so dimensionless) ;n :Manning's coefficient (unitless) Note: the symbol n is also used for porosity so it is important to be sure which term is implied. ;N :Number of days in the month ;Q<sub>p</sub> :Peak flow in units of volume per time (e.g. m<sup>3</sup>/s) ;R :Ratio of catchment impervious area (A<sub>i</sub>) to the practice permeable footprint area (A<sub>p</sub>). ''syn.'' I/P ratio. For [[green roofs]] and often [[permeable paving]] systems that do not receive drainage from external impervious areas this will be 0. For [[bioretention]], [[infiltration trenches]] and [[infiltration chambers]] receiving pavement runoff, it is recommended to be kept between 15 to 20.  ;R<sub>a</sub> :Existing rise of swale gradient (length, usually m) ;R<sub>b</sub> :Rise of compensation gradient for an enhanced swale (length, usually m) ;RVC<sub>T</sub> :Runoff volume control target (as outlined by MECP, units are mm) ;S<sub>0</sub> :Longitudinal slope (m/m, i.e. dimensionless) ;S<sub>T</sub> :Storage (m<sup>3</sup>) ;S<sub>x</sub> :Cross slope (m/m, i.e. dimensionless) ;SCF :Safety correction factor (dimensionless) ;t :Drainage time (usually in hrs) ;T :Temperature (°C) ;V :Volume (usually in m<sup>3</sup>) ;x :Perimeter of infiltration practice or swale x-section (m) ;y:Depth of water (lengthL, usually m or sometimes mm)

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