The EPA Storm Water Management Model (SWMM) is a computer software that simulates the rainfall-runoff-routing process in urban areas. It operates by dividing the study area into smaller subcatchment areas, where the hydrologic processes producing runoff are accounted for, including time-varying rainfall, evaporation, snow accumulation, depression storage, and more. The runoff is then routed through a network of pipes, channels, storage/treatment units, pumps, and regulators using hydraulic modeling techniques. The model can handle networks of any size, model different flow regimes, and use either kinematic wave or dynamic wave flow routing methods.
SWMM has been widely used in various applications, such as flood control, waste load allocation studies, and master planning of sewer collection systems. It is public domain software that can be freely copied and distributed, with the C engine code and Delphi graphical user interface code easily edited for custom features.
Applications:
- Design and sizing of drainage system components for flood control
- Sizing of detention facilities for flood control and water quality protection
- Flood plain mapping of natural channel systems
- Minimizing Combined Sewer Overflow (CSO) and Sanitary Sewer Overflow (SSO)
- Evaluating the impact of inflow and infiltration on sanitary sewer overflows
- Generating non-point source pollutant loadings for waste load allocation studies
- Evaluating the effectiveness of Best Management Practices (BMPs) and Low Impact Development (LID) practices
- Rainfall-runoff modeling of urban and rural watersheds
- Hydraulic and water quality analysis of storm, sanitary, and combined sewer systems
- Master planning of sewer collection systems and urban watersheds
- System evaluations associated with EPA regulations, such as NPDES permits, CMOM, and TMDL
- 1D and 2D predictions of flood levels and flooding volume
Hydrologic Processes Accounted for in SWMM:
- 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
- Capture and retention of rainfall/runoff by LID practices
Hydraulic Modeling Capabilities:
- Handle networks of unlimited size
- Use a variety of standard closed and open conduit shapes and natural channels
- Model special elements such as storage/treatment units, flow dividers, pumps, weirs, and orifices
- Apply external flows and water quality inputs from various sources
- Use 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.
