#LID Defaults from the EPA SWC

#LID Defaults from the EPA SWC

The following defaults are from the EPA Stormwater Calculator

A few of these parameters such as the capture ratio are not parameters in InfoSWMM Sustain

There are some additional points to keep in mind when applying LID controls to a site:
1.      The area devoted to Disconnection, Rain Gardens, and Infiltration Basins is assumed to come from the site’s collective amount of pervious land cover while the area occupied by Green Roofs, Street Planters and Porous Pavement comes from the site’s store of impervious area.

2.      Underdrains (slotted pipes placed in the gravel beds of Street Planter and Porous Pavement areas to prevent the unit from flooding) are not provided for. However since underdrains are typically oversized and placed at the top of the unit’s gravel bed, the effect on the amount of excess runoff flow bypassed by the unit is the same whether it flows out of the underdrain or simply runs off of a flooded surface.
3.      The amount of void space in the soil, gravel, and pavement used in the LID controls are listed in Table 4 below. They typically have a narrow range of acceptable values and results are not terribly sensitive to variations within this range.

Table 3. Editable LID parameters.

LID Type
Parameter
Default Value
Disconnection
Capture Ratio
100 %
Rain Harvesting
Cistern Size
100 gal
Cistern Emptying Rate
50 gal/day
Number of Cisterns
4 per 1,000 sq ft
Rain Gardens
Capture Ratio
5 %
Ponding Depth
6 inches
Soil Media Thickness
12 inches
Soil Media Conductivity
10 inches/hour
Green Roofs
Soil Media Thickness
4 inches
Soil Media Conductivity
10 inches/hour
Street Planters
Capture Ratio
6 %
Ponding Depth
6 inches
Soil Media Thickness
18 inches
Soil Media Conductivity
10 inches/hour
Gravel Bed Thickness
12 inches
Infiltration Basins
Capture Ratio
5 %
Basin Depth
6 inches
Porous Pavement
Capture Ratio
100 %
Pavement Thickness
4 inches
Gravel Bed Thickness
18 inches

Table 4. Void space values of LID media.

Property
LID Controls
Default Value
Soil Media Porosity
Rain Gardens, Green Roofs and Street Planters
45 %
Gravel Bed Void Ratio
Street Planters and Porous Pavement
75 %
Pavement Void Ratio
Porous Pavement
12 %

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