SWMM was first developed in 1971, and has since undergone several major upgrades since then. It continues to be widely used throughout the world for planning, analysis and design related to stormwater runoff, combined sewers, sanitary sewers, and other drainage systems in urban areas, with many applications in non-urban areas as well.
Running under Windows, SWMM provides an integrated environment for editing study area input data, running hydrologic, hydraulic and water quality simulations, and viewing the results in a variety of formats. These include color-coded drainage area and conveyance system maps, time series graphs and tables, profile plots, and statistical frequency analyses.
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 comprised of multiple time steps.
SWMM accounts for various hydrologic processes that produce runoff from urban areas. These include:
* time-varying rainfall
* evaporation of standing surface water
* snow accumulation and melting
* rainfall interception from depression storage
* infiltration of rainfall into unsaturated soil layers
* percolation of infiltrated water into groundwater layers
* interflow between groundwater and the drainage system
* nonlinear reservoir routing of overland flow
* runoff reduction via Low Impact Development (LID) controls.