Storm Water Management Model (SWMM)

Posted on: 1/04/2023 - Updated on: 1/04/2023

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EPA's Storm Water Management Model (SWMM) is used throughout the world for planning, analysis, and design related to stormwater runoff, combined and sanitary sewers, and other drainage systems. It can be used to evaluate gray infrastructure stormwater control strategies, such as pipes and storm drains, and is a useful tool for creating cost-effective green/gray hybrid stormwater control solutions.

SWMM is used for single event or long-term simulations of water runoff quantity and quality in primarily urban areas—although there are also many applications that can be used for drainage systems in non-urban areas. 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.


  • Hydraulic Modeling: SWMM 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. 
  • Accounting for Hydrologic Processes: SWMM accounts for various hydrologic processes that produce runoff from urban areas.
  • Pollutant Load Estimation: SWMM can estimate the production of pollutant loads associated with stormwater runoff.
  • Add-in Tool for Climate Projections: SWMM includes a software utility that allows future climate change projections to be incorporated into modeling. The SWMM Climate Adjustment Tool (SWMM-CAT) provides a set of location-specific adjustments derived from World Climate Research Programme global climate change models. SWMM-CAT accepts monthly adjustment factors for climate-related variables that could represent the potential impact of future climate changes.
  • Add-in Tool for Design Storm Wizard: This SWMM add-in tool will help you create a times series of rainfall intensities for a design storm of a given depth, duration, and return period. You can use from a variety of standard deign storm distributions and use Intensity-Duration-Frequency curve information if available. The result can be copied or saved for later use within the EPA Storm Water Management Model (SWMM). 

Typical Applications of SWMM:

  • Designing and sizing of drainage system components for flood control.
  • Sizing detention facilities and their appurtenances for flood control and water quality protection.
  • Mapping flood plains of natural channel systems—SWMM 5 is a FEMA-approved model for National Flood Insurance Program studies.
  • Designing control strategies for minimizing combined sewer overflows.
  • Evaluating the impact of inflow and infiltration on sanitary sewer overflows.
  • Generating nonpoint source pollutant loadings for waste load allocation.
  • Controlling site runoff using green infrastructure practices as low LID controls.
  • Evaluating the effectiveness of best management practices and low impact development for reducing wet weather pollutant loadings.


SWMM was developed to help support local, state, and national stormwater management objectives to reduce runoff through infiltration and retention, and help to reduce discharges that cause impairment of waterbodies.


Michelle Simon

Managing Organizations

The Environmental Protection Agency is an independent executive agency of the United States federal government tasked with environmental protection matters. The Environmental Protection Agency has ten Regional offices, each of which is responsible for the execution of the Agency's programs within several states and territories.