Notation

From LID SWM Planning and Design Guide
Revision as of 17:55, 22 April 2020 by Dean Young (talk | contribs)
Jump to: navigation, search
Ac 
Area of the catchmentThe land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale., whole contributing drainage areaThe total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds. (usually in m2).
Ai 
Area of imperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. cover within the catchmentThe land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale. (usually in m2).
Ap 
Area of the practice e.g. footprint area of a bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. cell (usually in m2)
Duration of the design storm event (in units of time, usually hrs)
dp 
Surface ponding depth of an infiltration practice (unit of length, usually mm or cm)
dm 
Filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. depth of a bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation., stormwater planterA vegetated practice that collects and treats stormwater through sedimentation and filtration. Contributions to water cycle/water balance are through evapotranspiration only; no infiltration. or soil cell practice (unit of length, usually mm or cm)
ds 
Storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. depth of an infiltration practice (unit of length, usually mm or cm)
dT 
Total depth of an infiltration practice (unit of length, usually cm or m)
Infiltration rateThe rate at which stormwater percolates into the subsoil measured in inches per hour., measured (usually mm/hr)
f'
Design infiltration rateThe rate at which stormwater percolates into the subsoil measured in inches per hour. (length per time, usually mm/hr) after application of safety correction factor (SCF)
Height (units of length)
Intensity of the design storm event (in units of depth/time, usually mm/hr)
Thornthwaite monthly heat index (-)
Thornthwaite annual heat index (-)
Length, e.g. of a reach, channel or swaleA shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades. (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)
Porosity, applies to aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. and other void-forming materials, filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. and native soils (unit is vol/vol, so dimensionless)
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
Qp 
Peak flow in units of volume per time (e.g. m3/s)
Ratio of catchmentThe land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale. imperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. area (Ai) to the practice footprint area (Ap). syn. I/P ratioThe ratio of the impervious catchment (drainage) area to the pervious (footprint) area of the receiving BMP.. For green roofs and often permeable paving systems that do not receive drainage from external imperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. areas this will be 0. For bioretention, infiltration trenches and infiltration chambers receiving pavement runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface., it is recommended to be kept between 15 to 20.
Ra 
Existing rise of swaleA shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades. gradient (length, usually m)
Rb 
Rise of compensation gradient for an enhanced swaleVegetated open channel, with check dams; designed to convey, treat and attenuate stormwater runoff. (length, usually m)
RVCT 
RunoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. 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)
Drainage timeThe period between the maximum water level and the minimum level (dry weather or antecedent level). (usually in hrs)
Temperature (°C)
Volume (usually in m3)
Perimeter of infiltration practice or swaleA shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades. x-section (m)
Depth of water (L, usually m or sometimes mm)