Open main menu

LID SWM Planning and Design Guide β

Notation

Revision as of 16:51, 22 April 2020 by Dean Young (talk | contribs)
Ac 
Area of the catchment, whole contributing drainage area (usually in m2).
Ap 
Area of the practice e.g. footprint area of a bioretention cell (usually in m2)
Depth e.g. of an infiltration practice (units of length, usually mm or m)
Infiltration rate (usually mm/hr)
height (units of length)
Thornthwaite monthly heat index (-)
Thornthwaite annual heat index (-)
Length, e.g. of a reach, channel or swale (usually in 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)
Manning's coefficient (unitless) Note: the symbol n is also used for porosity so it is important to be sure which term is implied.
Number of days in the month
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)
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)
time (usually in hrs)
Temperature (°C)
Volume (usually in m3)
Porosity, applies to aggregate and other void-forming materials, filter media and native soils (unit is vol/vol, so dimensionless)
Depth of water (L, usually m or sometimes mm)