1.   Purpose and objectives

     To provide effective tools for planning, design and operation of urban stormwater, combined sewer, and sanitary sewer systems and for management of urban nonpoint source runoff pollution.

2.   Description

     This program simulates rainfall, runoff, transport, and water quality processes in urban and some non-urban watersheds. Both single storm event and continuous simulation may be used to characterise the response of catchments to inputs of precipitation and related meteorological time series. Flow in open channels and closed conduits may be simulated.  

     The Runoff Block converts precipitation, from one or more gages, to runoff using a non-linear reservoir method, with infiltration losses based on the Horton or Green-Ampt equations. Water that infiltrates may be optionally routed through groundwater storage. Continuous moisture accounting is performed, and snowmelt may be simulated as well as infiltration/inflow and many other options. Up to a few thousand subcatchments and channel/pipes may be used to discretise the overall catchment.

     Other functions include flow and quality routing in channels and conduits; backwater effects, reverse flow, looped connections, surcharging, pressure flow, weirs, orifices, culverts, pumps, time-variable regulator settings and storage routing. Natural channel sections, bridges, and best management practices as well as other options may be simulated.

3.   Input

     Input data include: historic or synthetic long-term or single-event precipitation hyetographs and optional ancillary meteorological time series such as evaporation and wind speeds; catchment topography, imperviousness, shape factor, depression storage, Manning roughness, and infiltration 
parameters; optional data for simulation of groundwater flow, snowmelt, infiltration/inflow etc.; channel/pipe and drainage network information.  Input for the basic EPA Fortran engine must be prepared in the form of input data files using a standard text editor.  
        

4.   Output

     Output is in the form of hydrographs, pollutographs (concentration vs. time), and time series of other state variables such as stages, volumes and loads, and in the form of statistical summaries. Various continuity checks are performed

5.   Operational requirements and restrictions

     The program is developed for MS-DOS or Microsoft Windows-based (95/98/NT) microcomputers. The program runs best in a fast Pentium environment. It is written in Fortran 77 with some extensions to Fortran 90. Minimum storage of about 20 Mb is required. The basic Fortran engine is in the public domain. Source code is provided.  

6.   Form of presentation

     The Fortran engine may be downloaded at no charge from the World Wide Web or obtained similarly by ftp. The most current version of the model is provided at: http://www.ccee.orst.edu/swmm

     This site contains links to the Environmental Protection Agency and to private party sites that provide graphical user interfaces (GUIs).  

7.   Operational experience

     Extensive. Although used primarily in the United States and Canada, a world-wide user base exists of several thousand engineers, since 1971.  

8.   Originator and technical support

     The original program was developed during 1969-71 by Metcalf and Eddy, Inc., Camp, Dresser and McKee, Inc. and the University of Florida, under the sponsorship of the U.S. Environmental Protection Agency. It is currently (1999) maintained for the EPA at Oregon State University (OSU).  Technical support may be obtained from the swmm-users Internet discussion group and from the current program developers.  

9.   Availability

     The HOMS National Reference Centre for the USA is the National sponsor. The basic program (Fortran engine, source code, and example files) may be downloaded from various Web or ftp sites for free. Standard handling fee is charged for documentation. Useful graphical output is only available 
via GUIs developed by private firms, for which addresses and web links are provided on the OSU web site.

10.  Conditions on use

     The basic Fortran engine is non-proprietary and may be applied at the user’s own risk at no charge and with no conditions.