This document provides instructions for adding low impact development (LID) controls to subcatchments in EPA's SWMM 5.1 hydrological model. It describes how to design 6 types of LID controls by specifying their layer parameters. Tables are provided giving parameter values for green roofs, permeable pavement, bio-retention cells, infiltration trenches, rain barrels, and rain gardens. The document then explains how to assign these designed LID controls to different subcatchments and input their planning parameters.

2. • Based on the given input data file we will add LID (Low Impact Development)
options for subcatchments
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3. • EPA’s SWMM 5.1 has been extended to model the hydrologic performance
of specific types of low impact development (LID) controls.
• LID controls that you can choose include 7 green infrastructure practices
1. Permeable pavement
2. Rain gardens
3. Green roofs
4. Street planters
5. Rain barrels
6. Infiltration trenches
7. Vegetative swales (not optional in WMAM)
• You will edit 6 types of LID structures by using the LID control option of
EPA SWMM5.1
• Follow the instructions (step 1 to step 7) to enter all values
• The following tables are information of the LID control you will edit
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4. Control name LID type Layer Parameter Value
GR_your initial Green Roof
Surface
Berm Height 3
Vegetation Volume Fraction 0.2
Surface Roughness 0.1
Surface Slope 1.0
Soil
Thickness 6
Porosity 0.5
Field Capacity 0.2
Wilting Point 0.1
Conductivity 0.5
Conductivity Slope 10
Suction Head 3.5
Drainage Mat
Thickness 1
Void Fraction 0.5
Roughness 0
<Table 1> Information of green roof
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5. <Table 2> Information of permeable pavement
Control name LID type Layer Parameter Value
PP_your initial Permeable Pavement
Surface
Berm Height 1
Vegetation Volume Fraction 0.1
Surface Roughness 0.02
Surface Slope 2
Pavement
Thickness 8
Void Ratio 0.15
Impervious Surface Fraction 0
Permeability 100
Clogging Factor 0
Storage
Thickness 12
Void Ratio 0.75
Seepage Rate 0.2
Clogging Factor 0
Underdrain
Flow Coefficient 0
Flow Exponent 0.5
Offset Height 0
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6. <Table 3> Information of bio-retention cell
Control name LID type Layer Parameter Value
BC_your initial Bio-Retention Cell
Surface
Berm Height 6
Vegetation Volume Fraction 0.0
Surface Roughness 0.2
Surface Slope 0
Soil
Thickness 12
Porosity 0.5
Field Capacity 0.2
Wilting Point 0.1
Conductivity 0.5
Conductivity Slope 10
Suction Head 3.5
Storage
Thickness 12
Void Ratio 0.5
Seepage Rate 0.5
Clogging Factor 0.2
Underdrain
Flow Coefficient 0
Flow Exponent 1
Offset Height 0.5
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7. <Table 4> Information of infiltration trench
Control name LID type Layer Parameter Value
IT_your initial Infiltration Trench
Surface
Berm Height 0.0
Vegetation Volume Fraction 0.0
Surface Roughness 0.24
Surface Slope 0.4
Storage
Thickness 36
Void Ratio 0.4
Seepage Rate 0.2
Clogging Factor 0
Underdrain
Flow Coefficient 0
Flow Exponent 0.5
Offset Height 0
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8. <Table 5> Information of rain barrel
Control name LID type Layer Parameter Value
RB_your initial Rain Barrels
Storage Berm Height 48
Underdrain
Flow Coefficient 1
Flow Exponent 0.5
Offset Height 0
Drain Delay 6
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9. <Table 6> Information of rain garden
Control name LID type Layer Parameter Value
RG_your initial Rain Garden
Surface
Berm Height 6
Vegetation Volume Fraction 0.0
Surface Roughness 0.0
Surface Slope 0.0
Soil
Thickness 12
Porosity 0.5
Field Capacity 0.2
Wilting Point 0.1
Conductivity 0.5
Conductivity Slope 10
Suction Head 2.5
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10. • Select LID Controls from the project browser (under Hydrology)
Step 1
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11. • Left click the add button or select Project -> Add a new LID Control
from the main menu
Step 2
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12. • Enter the Control Name for the LID structure
Step 3
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13. • Choose the type of the LID structure
Step 4
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14. • Enter the parameter values of the surface layer
Step 5
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15. • To enter the parameter values of the Soil, Storage, and Underdrain layer
click the tab of the layer
Step 6
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16. • Follow step 1~6 and use the information in table 1~6 to edit the LID control
• After you have entered all the values, you can find your designed LID controls
• Now you will plan the subcatchment area with the designed LID structures
• Step 7 to step 11 shows how to edit the LID Usage Editor
• Follow the instructions from (step 7 ~ 11) and use the following information to
complete the editing process
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17. Subcatchment LID Process
S1 Infiltration trench
S1 Rain barrel
S4 Bio-retention cell
S5 Permeable pavement
S5 Green roof
S6 Rain garden
<Table 7> LID controls for subcatchments
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18. Subcatchment LID Process
Area of
Each Unit
Numb
of Unit
Surface
Width
per Unit
% Initially
Saturated
% of
Imperv
Area
Treated
Return
all
outflow
to perv
S1 Infiltration trench 2320000 4 133 0 40 -
S1 Rain barrel 100 32 0 0 17 Check
S4 Bio-retention cell 47500 500 0 10 50 -
S5 Permeable pavement 3828720 1 683 0 0 -
S5 Green roof 1840000 12 136 0 0 -
S6 Rain garden 1650000 1 0 15 5 -
<Table 8> LID planning parameters for each structure
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19. • Open the editing window (properties) of one of the subcatchments
Step 7
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20. • Left click on the box in LID controls
Step 8
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21. • Left click Add to open the LID usage editor
Step 9
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22. • Select the LID control name
• Enter the planning parameter values for the selected LID structure
Step 10
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23. • If you check the LID Occupies Full Subcatchment, the LID structure will
automatically calculate the Area of each unit as it is designed
Step 11
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