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 in urban areas. There are many applications for drainage systems in non-urban areas as well.

SWMM is a dynamic hydrology-hydraulic water quality simulation model. It is used for single event or long-term simulation of runoff quantity and quality from primarily urban areas. The runoff component operates on a collection of sub-catchment areas that receive precipitation and generate runoff and pollutant loads. The routing portion 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 sub-catchment. It tracks the flow rate, flow depth, and quality of water in each pipe and channel during a simulation period made up of multiple time steps.

A recent add-on for SWMM, the Climate Adjustment Tool, enables users to add climate projections based on the Intergovernmental Panel on Climate Change’s climate change scenarios to existing simulations.

SWMM 5 has recently been extended to model the hydrologic performance of specific types of low-impact development (LID) controls. The LID controls that the user can choose include the following seven green infrastructure practices:

• Permeable pavement
• Rain gardens
• Green roofs
• Street planters
• Rain barrels
• Infiltration trenches
• Vegetative swales

The 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 latter includes:

• 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.