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Storm Water Management Model (SWMM)

Screen shot of the EPA SWMM 5 Graphical User Interface. Please Contact Lewis Rossman at rossman.lewis@epa.gov or (513) 569-7603 for a detailed description. Click on image for a larger view.

Version 5.0.022 with Low Impact Development (LID) Controls

Description

EPA's Storm Water Management Model (SWMM) is 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.

This general purpose urban hydrology and conveyance system hydraulics software is a dynamic rainfall-runoff 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 made within each subcatchment,
  • and the flow rate, flow depth, and quality of water in each pipe and channel

during a simulation period made up of multiple time steps. EPA has recently extended SWMM 5 to explicitly model the hydrologic performance of specific types of low impact development (LID) controls, such as:

  • porous pavement,
  • rain gardens,
  • green roofs,
  • street planters,
  • rain barrels,
  • infiltration trenches, and
  • vegetative swales.

The updated model allows engineers and planners to accurately represent any combination of LID controls within a study area to determine their effectiveness in managing stormwater and combined sewer overflows.
Running under Windows, SWMM 5 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.

The formats include:

  • color-coded drainage area and conveyance system maps,
  • time series graphs and tables,
  • profile plots, and
  • statistical frequency analyses.

SWMM 5 was produced in a joint development effort with CDM, Inc., a global consulting, engineering, construction, and operations firm.

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Capabilities

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.

Spatial variability in all of these processes is achieved by dividing a study area into a collection of smaller, homogeneous 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 channels
  • model special elements such as storage/treatment units, 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 kinematic wave or full dynamic wave flow routing methods
  • model various flow regimes, such as backwater, surcharging, reverse flow, and surface ponding
  • apply user-defined dynamic control rules to simulate the operation of pumps, orifice openings, and weir crest levels

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:

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