Notation
Revision as of 17:39, 22 April 2020 by Dean Young (talk | contribs)
- Ac
- Area of the catchment, whole contributing drainage area (usually in m2).
- Ai
- Area of impervious cover within the catchment (usually in m2).
- Ap
- Area of the practice e.g. footprint area of a bioretention cell (usually in m2)
- d
- Depth e.g. of an infiltration practice (units of length, usually mm or m)
- f
- Infiltration rate (usually mm/hr)
- h
- height (units of length)
- 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
- 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
- x
- Perimeter of infiltration practice or swale x-section (m)
- f'
- Design infiltration rate (length per time, usually mm/hr) after application of safety correction factor (SCF)
- Qp
- Peak flow in units of volume per time (e.g. m3/s)
- R
- Ratio of catchment (Ac) to the practice footprint area (Ap). syn. I/P ratio. For green roofs (and often permeable paving systems) this will be 1:1. In bioretention it may be 15 or 20 to 1.
- Ra
- Existing rise of swale gradient (length, usually m)
- Rb
- Rise of compensation gradient for an enhanced swale (length, usually m)
- RVCT
- Runoff volume control target (as outlined by MECP, units are mm)
- S0
- Longitudinal slope (m/m, i.e. dimensionless)
- ST
- Storage (m3)
- Sx
- Cross slope (m/m, i.e. dimensionless)
- SCF
- Safety correction factor (dimensionless)
- t
- time (usually in hrs)
- T
- Temperature (°C)
- V
- Volume (usually in m3)
- n
- Porosity, applies to aggregate and other void-forming materials, filter media and native soils (unit is vol/vol, so dimensionless)
- y
- Depth of water (L, usually m or sometimes mm)