LID parameters have been set based on the 2010 Low Impact Development Stormwater Management Planning and Design Guide. Certain parameters are available for most LIDs. These parameters are given in Table 3-11.

TABLE 3-11 LIDs COMMON PARAMETERS

Parameter Name Description Default Value
WIDTH Width of LID layer (m) 1
LENGTH Length of LID layer (m) 1
HEIGHT Depth of LID layer (m) 1
POROSITY Fraction of void space (pores) in the storage layer 0.4
Min Drawdown Time Drawdown time (hour) 24
ENGINEERED SOIL AND NATIVE SOIL
SOIL TEXTURE Description of soil base on relative content of sand, silt, clay particles Loam
INFILTRATION RATE Rate with which water moves through porous materials (m/hour) 0.051
Total Porosity The volumetric water content of a soil (volume of water per total volume) when its pore spaces are at saturated, vol/vol Only available for continuous when infiltration type is set as Green ampt.
FIELD CAPACITY The amount of water a well-drained soil holds after free water has drained off, or the maximum amount it can hold against gravity, vol/vol Only available for continuous when infiltration type is set as Green ampt.
WILTING POINT The soil moisture content at which plants can no longer obtain enough moisture to meet transpiration requirements, vol/vol Only available for continuous when infiltration type is set as Green ampt.
SATURATED K Saturated Hydraulic Conductivity (mm/day) Only available for continuous when infiltration type is set as Green ampt.
SUCTION HEAD Wetting Front Suction Head Only available for continuous when infiltration type is set as Green ampt.
UNDERDRAIN
TYPE Orifice Equation
DISCHARGE CURVE Depth discharge curve for the underdrain, depth is defined from the bottom of the storage layer. Users can enter 0 discharge up to the invert of the subdrain, if perched.
DIAMETER Diameter of underdrain pipe (mm) 250
MANNING COEFFICIENT Manning’s Roughness Coefficient 0.013
LENGTH Length of underdrain (m) 4
MAXIMUM FLOW Maximum flow allowed through underdrain (m³/s)
SLOPE Slope of the underdrain (m/m) 0.001
PERFORATIONS
PERFORATIONS/ROW Number of perforations per row of perforations (#) 10
ORIFICE COEFFICIENT Orifice coefficient used in orifice equation 0.63
MINIMUM SPACING Minimum spacing between perforations (mm) 25
DIAMETER Diameter of perforations (mm) 25
NUMBER OF ROWS Number of rows of perforations (#) 4
SAFETY FACTOR Safety or Clogging factor applied to subdrain outflow (#) 1

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