Introduction to the USEPA’s
Storm Water Management
Model (SWMM 5.0)
David Rosenberg
CEE 5460 – Water Resources
Engineering
Learning Objectives
• Describe model components and inputs
• Enter rainfall, catchment, and other input data
• Generate the outflow hydrograph for a design
storm over a catchment
• http://www.epa.gov/nrmrl/wswrd/wq/models/swmm/
CEE 5460
2
What Is SWMM?
• Distributed, dynamic rainfall-runoff simulation model
• Simulate single or long-term (continuous) events
• Runoff
quantity
and quality
from
primarily
urban
areas
3
What Is SWMM?
• Distributed, dynamic rainfall-runoff simulation model
• Simulate single or long-term (continuous) events
• Runoff
quantity
and quality
from
primarily
urban
areas
4
Typical Uses
• Design and size drainage system components
including detention facilities
• Map flood plains of natural channel systems
• Control combined and sanitary sewer overflows
• Generate non-point source pollutant loadings for
wasteload allocation studies
• Evaluate BMPs and LIDs for sustainability goals
CEE 5460
David Rosenberg
5
Processes Simulated
(grey = focus for CEE 5460)
CEE 5460
David Rosenberg
6
Model Components
CEE 5460
Visual
Non-Visual
Rain gage
Subcatchment
Junction
Outfall
Divide
Storage unit
Conduit
Pump
Orafice
Weir
Outlet
•
•
•
•
•
•
•
•
•
•
•
•
Climate data
LID controls
Snow packs
Aquifers
Unit hydrographs
Transects
External inflows
Control rules
Pollutants
Land uses
Treatment
Time-series
David Rosenberg
7
Representing land use in a
subcatchment
Pervious area
Impervious area
Impervious area
with depression
with no storage
storage
CEE 5460
Outlet
David Rosenberg
8
File
menu
Working with SWMM
Tools
Object
toolbar
Backdrop
image
Visual
objects
Edit objects
Using SWMM
Step
1. Start a new project
2. Set project defaults
Location
File menu
Project=>defaults…
3. Set display settings
Tools=>Map display
settings…
4. Add visual objects to the map
5. Enter data for visual objects
6. Set up simulation
Object toolbar
Several ways
Data tree=>Options
7. Run simulation
8. View results
9. Modify assumptions
Project=>Run sim.
Tool icons
Several ways
CEE 5460
David Rosenberg
10
2. Set project defaults
• Select
Infiltration
model
David Rosenberg
11
4. Add visual objects
• Click an object from the object tool bar
• Place it on the map
• For conduits,
click the start
object, then
the
destination
object
Subcatchment
Outflow
Conduit
Junction
Rain gage
5. Enter data
• Right-click an object =>
select properties
• For subcatchments
–
–
–
–
–
Assign a rain gage
Assign an outlet
Enter data fields
Explanations are at the bottom!
Enter the Curve Number (for
SCS method) by doubleclicking Infiltration
David Rosenberg
13
5. Enter data (continued)
Precipitation
• Add a rain gage
• Define the timeseries
David Rosenberg
14
6. Simulation Set up
• Select
Options=>General
• Select Process Models,
Infiltration method, and
Routing Model (steady
flow for PBL-2)
• Set Dates of simulation
period
• Set computational time
step
David Rosenberg
15
7. Run the Simulation
• Select Project => Run Simulation
• Or click
David Rosenberg
16
7. Run the Simulation (cont.)
• Successful when continuity error is low (< 10%)
David Rosenberg
17
8. View Results
Graphs
Tables
Statistics
etc.
8. View Results (cont.)
CEE 5460
David Rosenberg
19
Example 1. Generate the runoff hydrograph
from Lundstrum Park, Logan
• Use last Thursday’s
6-hr duration Layton
storm with a 10-year
recurrence interval
Lunstrum Park (blue)
• 18.4 acres
• 1,440 ft length to
divide
• Dense grass
• 40’ road width
Location
Elevation
(ft.)
East (canal)
4,855
West (1600 E)
4,810
Example 1. Questions to Answer
1. What inputs did you change/enter?
2. What is the peak flow?
3. When does the peak flow occur?
4. Why do these values differ from our example
from Tuesday?
Hint 1: What processes does SWMM simulate? SCS?
Hint 2: Look at the precipitation intensity values
CEE 5460
David Rosenberg
21
Example 1. Answers
1. Set the rain gage and outlet
2. Area = 18.4 ac
3. Width = Area/length to divide
4. % slope = 3.125%
5. %Imperv = 3%
6. N-imperv = 0.011 (from manual)
7. N-perv = 0.15 (from manual)
8. Dstore-imperv = 0.075 (manual)
9. Dstore-Perv = 0.15 (from manual)
10. Curve Number = 61 (from Sept 27)
Example 1. Answers (cont)
10. Set simulation time step
11. Resulting subcatchment runoff
hydrograph
David Rosenberg
23
Model Limitations
• Only for small-scale, urban watersheds
• Not applicable to forested areas or irrigated
cropland
• Cannot be used with highly disaggregated (e.g.,
daily) rainfall data
• It’s an analysis tool, not an automated design tool
CEE 5460
David Rosenberg
24
Conclusions
• SWMM simulates runoff from urban watersheds
• Includes precipitation, pervious and impervious
land cover, depression storage, infiltration, etc.
• Can include pipes, channels, weirs, orafices,
drainage systems, curbs, constructed features, and
• Detention basins (next week)
CEE 5460
David Rosenberg
25
Additional Resources
• Model downloads and documentation
http://www.epa.gov/nrmrl/wswrd/wq/models/swmm/
• SWMM User’s Manual
Yes, read it!
Appendices provide suggested model inputs
• SWMM-USERS List Server
Email: [email protected]
With the statement in the body
SUBSCRIBE SWMM-USERS [first name] [last name]
CEE 5460
David Rosenberg
26