#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 %
|
