Storm Water Management Model

From Wikipedia, the free encyclopedia
Jump to: navigation, search

The United States Environmental Protection Agency (EPA) Storm Water Management Model (SWMM)[1][2][3][4][5][6][7] is a dynamic rainfall-runoff-subsurface runoff simulation model used for single-event to long-term (continuous) simulation of the surface/subsurface hydrology quantity and quality from primarily urban/suburban areas. The hydrology component of SWMM operates on a collection of subcatchment areas divided into impervious and pervious areas with and without depression storage to predict runoff and pollutant loads from precipitation, evaporation and infiltration losses from each of the subcatchment. In addition Low Impact Development (LID) and Best Management Practice (BMP) areas on the subcatchment can be modeled to reduce the impervious and pervious runoff. The routing or hydraulics section of SWMM transports this water and possible associated water quality constituents through a system of closed pipes, open channels, storage/treatment devices, ponds, storages, pumps, orifices, weirs, outlets, outfalls and other regulators. SWMM tracks the quantity and quality of the flow generated within each subcatchment, and the flow rate, flow depth, and quality of water in each pipe and channel during a simulation period composed of multiple fixed or variable time steps. The water quality constituents such as water quality constituents can be simulated from buildup on the subcatchments through washoff to a hydraulic network with optional first order decay and linked pollutant removal, Best Management Practice (BMP) and Low Impact Development (LID) removal and treatment can be simulated at selected storage nodes. SWMM is one of the hydrology transport models which the EPA and other agencies have applied widely throughout North America and through consultants and universities throughout the world.

Program Description[edit]

The EPA Storm Water Management Model (SWMM) is a dynamic rainfall-runoff-routing simulation model used for single event or long-term (continuous) simulation of runoff quantity and quality from primarily urban areas. The runoff component of SWMM operates on a collection of subcatchment areas that receive precipitation and generate runoff and pollutant loads. The routing portion of SWMM transports this runoff through a system of pipes, channels, storage/treatment devices, pumps, and regulators. SWMM tracks the quantity and quality of runoff generated within each subcatchment, and the flow rate, flow depth, and quality of water in each pipe and channel during a simulation period divided into multiple time steps.

EPA SWMM is public domain software that may be freely copied and distributed.


SWMM was first developed between 1969–1971 and has undergone several major upgrades since those years. The major upgrades were: (1) Version 2 in 1975, (2) Version 3 in 1981 and (3) Version 4 in 1988. The current SWMM edition, Version 5.1, is a complete re-write of the previous Fortran releases in the programming language C, and it can be run under Windows XP, Windows Vista and Windows 7 and with a recomplilation under Unix. The code for SWMM5 is open source and public domain code that can be downloaded from the EPA Web Site.

SWMM History
Release Date Versions Developers FEMA LID
10/09/2014 SWMM 5.1.007 EPA Yes Yes
06/02/2014 SWMM 5.1.006 EPA Yes Yes
03/27/2014 SWMM 5.1.001 EPA Yes Yes
04/21/2011 SWMM 5.0.022 EPA Yes Yes
08/20/2010 SWMM 5.0.019 EPA Yes Yes
08/17/2005 SWMM 5.0.005 EPA, CDM Yes No
11/30/2004 SWMM 5.0.004 EPA, CDM No No
11/25/2004 SWMM 5.0.003 EPA, CDM No No
10/26/2004 SWMM 5.0.001 EPA, CDM No No
2001–2008 SWMM5 EPA, CDM No No
1988–2004 SWMM4 UF, OSU, CDM No No
1981–1988 SWMM3 UF, CDM No
1975–1981 SWMM2 UF No No
1969–1971 SWMM1 UF, CDM, M&E No No

EPA SWMM 5 provides an integrated graphical environment for editing watershed input data, running hydrologic, hydraulic, real time control and water quality simulations, and viewing the results in a variety of graphical formats. These include color-coded thematic drainage area maps, time series graphs and tables, profile plots, scatter plots and statistical frequency analyses.

This latest re-write of EPA SWMM was produced by the Water Supply and Water Resources Division of the U.S. Environmental Protection Agency's National Risk Management Research Laboratory with assistance from the consulting firm of CDM Inc under a Cooperative Research and Development Agreement (CRADA). SWMM 5 is used as the computational engine for many modeling packages plus components of SWMM5 are in other modeling packages. The major modeling packages that use all or some of the SWMM5 components are shown in the Vendor section. The update history of SWMM 5 from the original SWMM 5.0.001 to the current version SWMM 5.1.007 can be found at the EPA Download in the file epaswmm5_updates.txt. SWMM 5 was approved FEMA Model Approval Page in May 2005 with this note about the versions that are approved on the FEMA Approval Page SWMM 5 Version 5.1.007 (May 2005) and up. SWMM 5 is used as the computational engine for many modeling packages plus components of SWMM5 are in other modeling packages.

Model parameters[edit]

The simulated model parameters for subcatchments are surface roughness, depression storage, slope, flow path length; for Infiltration: Horton: max/min rates and decay constant; Green-Ampt: hydraulic conductivity, initial moisture deficit and suction head; Curve Number: NRCS (SCS) Curve number; All: time for saturated soil to fully drain; for Conduits: Manning’s roughness; for Water Quality: buildup/washoff function coefficients, first order decay coefficients, removal equations. A study area can be divided into any number of individual subcatchments, each of which drains to a single point. Study areas can range in size from a small portion of a single lots up to thousands of acres. SWMM uses hourly or more frequent rainfall data as input and can be run for single events or in continuous fashion for any number of years.

Hydrology and Hydraulics Capabilities[edit]

SWMM 5 accounts for various hydrologic processes that produce surface and subsurface runoff from urban areas. These include:

Time-varying rainfall for an unlimited number of raingages for both design and continuous hyetographs evaporation of standing surface water on watersheds and surface ponds snowfall accumulation, plowing and melting rainfall interception from depression storage in both impervious and pervious areas infiltration of rainfall into unsaturated soil layers percolation of infiltrated water into groundwater layers interflow between groundwater and pipes and ditches nonlinear reservoir routing of watershed overland flow.

Spatial variability in all of these processes is achieved by dividing a study area into a collection of smaller, homogeneous watershed or subcatchment areas, each containing its own fraction of pervious and impervious sub-areas. Overland flow can be routed between sub-areas, between subcatchments, or between entry points of a drainage system.

SWMM also contains a flexible set of hydraulic modeling capabilities used to route runoff and external inflows through the drainage system network of pipes, channels, storage/treatment units and diversion structures. These include the ability to:

handle drainage networks of unlimited size use a wide variety of standard closed and open conduit shapes as well as natural or irregular channels model special elements such as storage/treatment units, outlets, flow dividers, pumps, weirs, and orifices apply external flows and water quality inputs from surface runoff, groundwater interflow, rainfall-dependent infiltration/inflow, dry weather sanitary flow, and user-defined inflows utilize either steady, kinematic wave or full dynamic wave flow routing methods model various flow regimes, such as backwater, surcharging, pressure, reverse flow, and surface ponding apply user-defined dynamic control rules to simulate the operation of pumps, orifice openings, and weir crest levels

In addition to modeling the generation and transport of runoff flows, SWMM can also estimate the production of pollutant loads associated with this runoff. The following processes can be modeled for any number of user-defined water quality constituents:

Dry-weather pollutant buildup over different land uses pollutant washoff from specific land uses during storm events direct contribution of wet and dry rainfall deposition reduction in dry-weather buildup due to street cleaning reduction in washoff load due to BMP's and LID's entry of dry weather sanitary flows and user-specified external inflows at any point in the drainage system routing of water quality constituents through the drainage system reduction in constituent concentration through treatment in storage units or by natural processes in pipes and channels.

Low Impact Development (LID) Components[edit]

The Low Impact Development (LID) function is new to SWMM 5.0.019/20/21/22 and we have run many configurations and found no problem for the hydrology and hydraulics. It is integrated within the subcatchment and allows further refinement of the overflows, infiltration flow and evaporation in Rain Barrels, Vegetative Swales, Porous Pavement, Bio Retention Cell and Infiltration Trench.

You can define a variety of sub processes in each LID such as: Surface, Pavement, Soil, Storage, and Drain.

Each type of LID has limitations on the type of sub process allowed by SWMM 5. It has a good report feature and you can have a LID summary report in the rpt file and an external report file in which you can see the surface depth, soil moisture, storage depth, surface inflow, evaporation, surface infiltration, soil percolation, storage infiltration, surface outflow and the LID continuity error. You can have multiple LID's per subcatchment and we have had no issues having many complicated LID sub networks and processes inside the Subcatchments of SWMM 5 or any continuity issues not solvable by a smaller wet hydrology time step. The types of SWMM 5 LID compartments are: Storage, Underdrain, Surface, Pavement and Soil. A Bio Retention cell has Storage, Underdrain and Surface Compartments. An Infiltration Trench LID as Storage, Underdrain and Surface Compartments. A Porous Pavement LID has Storage, Underdrain and Pavement Compartments. A Rain Barrel has only Storage and Underdrain Compartments and a Vegatative Swale LID has a single Surface Compartment. Each type of LID shares different underlying compartment objects in SWMM 5.

New as of July 2013, the EPA's National Stormwater Calculator is a Windows desktop application that estimates the annual amount of rainwater and frequency of runoff from a specific site anywhere in the United States. Estimates are based on local soil conditions, land cover, and historic rainfall records. The Calculator accesses several national databases that provide soil, topography, rainfall, and evaporation information for the chosen site. The user supplies information about the site's land cover and selects the types of low impact development (LID) controls they would like to use.

Integrated Hydrology/Hydraulics[edit]

One of the great advances in SWMM 5 was the integration of Urban/Suburban Subsurface Hydrology with the Hydraulic computations of the drainage network. This advance is a tremendous improvement over the separate Subsurface Hydrologic and Hydraulic computations of the previous versions of SWMM because it allows the modeler to conceptually model the same interactions that occur physically in the real open channel/shallow aquifer environment. The SWMM 5 numerical engine calculates the surface runoff, subsurface hydrology and assigns the current climate data at either the wet or dry hydrologic time step. The hydraulic calculations for the links, nodes, control rules and boundary conditions of the network are then computed at either a fixed or variable time step within the hydrologic time step by using interpolation routines and the simulated hydrologic starting and ending values.

Figure 1. SWMM 5's QA/QC Master Example Network. This one network includes examples 1 through 7 from the SWMM 3 and SWMM 4 Manuals

An example of this integration was the collection of the disparate SWMM 4 link types in the Runoff, Transport and Extran Blocks to one unified group of closed conduit and open channel link types in SWMM 5 and a collection of Node types.

SWMM5 Components[edit]

The SWMM 5.0.001 to 5.1.001 main components are: rain gages, watersheds, lid/bmp, nodes, links, pollutants, landuses, time patterns, curves, time series, controls, transects, aquifers, unit hydrographs, snowmelt and shapes. Other related objects are the types of Nodes and the Link Shapes. The purpose of the objects is to simulate the major components of the hydrologic cycle, the hydraulic components of the drainage, sewer or stormwater network and the buildup/washoff functions that allow the simulation of water quality constituents. A watershed simulation starts with a precipitation time history.

The major overall components are called in the SWMM 5 input file and C code of the simulation engine: gage, subcatch, node, link, pollut, landuse, timepattern, curve, tseries, control, transect, aquifer, unithyd, snowmelt, shape and lid. The subsets of possible nodes are: junction, outfall, storage and divider. Storage Nodes are either tabular with a depth/area table or a functional relationship between area and depth. Possible node inflows include: external_inflow, dry_weather_inflow, wet_weather_inflow, groundwater_inflow, rdii_inflow, flow_inflow, concen_inflow, and mass_inflow. The dry weather inflows can include the possible patterns: monthly_pattern, daily_pattern, hourly_pattern and weekend_pattern.

Figure 2. SWMM 5's LID Processes include unlimited Low Impact Development or BMP Objects per Subcatchment.

SWMM 3,4 to 5 converter[edit]

The SWMM 3 and SWMM 4 converter can convert up to two files from the earlier SWMM 3 and 4 versions at one time to SWMM 5. Typically you would convert a Runoff and Transport file to SWMM 5 or a Runoff and Extran File to SWMM 5. If you have a combination of a SWMM 4 Runoff, Transport and Extran network then you will have to convert it in pieces and copy and paste the two data sets together to make one SWMM 5 data set. The x,y coordinate file is only necessary if you do not have existing x, y coordinates on the D1 line of the SWMM 4 Extran input data[ set. You can use the command File=>Define Ini File to define the location of the ini file. The ini file will save your conversion project input data files and directories.

SWMM Platforms[edit]

There are a number of software packages that utilize the SWMM5 platform. These include:

See also[edit]


  1. ^ Metcalf and Eddy, Water Resources Engineers, and University of Florida 1971. Storm Water Management Model, US EPA, Washington, D.C. Vol. I - Final Report, 11024DOC 7/71. Vol. II - Verification and Testing, 11024DOC 8/71. Vol. III - User's Manual, 11024DOC 9/71. Vol. IV - Program Listing, 11024DOC 10/71.
  2. ^ Huber, W. C., J. P. Heaney, M. A. Medina, W. A. Peltz, H. Sheikh, and G. F. Smith. 1975. Storm Water Management Model User’s Manual, Version II. U.S. Environmental Protection Agency, Cincinnati, Ohio.
  3. ^ Huber, W. C., J. P. Heaney, S. J. Nix, R. E. Dickinson, and D. J. Polmann, 1981. Storm Water Management Model. User's Manual Ver. III, U.S. Environmental Protection Agency
  4. ^ Huber, W. C. and R. E. Dickinson, 1988, Storm Water Management Model. User's Manual Ver. IV, U.S. Environmental Protection Agency
  5. ^ Roesner, L.A., R.E. Dickinson and J.A. Aldrich (1988) Storm Water Management Model – Version 4: User’s Manual – Addendum 1 EXTRAN; Cooperative Agreement CR-811607; U.S.EPA; Athens, Georgia.
  6. ^ Rossman, Lewis A., Storm Water Management Model User’s Manual, EPA/600/R-05/040, U.S. Environmental Protection Agency, Cincinnati, OH (June 2007)
  7. ^ Rossman, Lewis A., Storm Water Management Model Quality Assurance Report, Dynamic Wave Flow Routing, EPA/600/R-06/097, September 2006

SWMM 5 Vendors[edit]

External links[edit]