SWMM

Pollutant loads are reduced by applying a BMP removal factor, or percentage removal, entered by the user. When modeling the pollutant transport through the conveyance network, the user is also able to apply treatment at any location of the network. The user can specify the treatment as either a concentration remaining after treatment or a percentage removal. Street sweeping removal efficiencies are based on values obtained from Demonstration of Non-Point Pollution Abatement Through Improved Street Cleaning Practices (Pitt, 1979).

The user is required to load precipitation as a time series, either directly into the program or through an external file. Dry weather or point source contributions can be incorporated using time series or monthly values. Evapotranspiration can be loaded into the model as either a single constant or a set of monthly averages. Temperature and wind speed are optional inputs that are required for snowmelt calculations.

The user will also need to specify subcatchment, drainage system, and BMP information. Drainage system information can be loaded into the model as a CAD or GIS file.

Output is in the form of a report, a time series, a graph, or displayed on a map within the program, depending on the desired result. The output can include the subcatchment runoff, BMP performance, a groundwater summary, and the pollutant loads.

• Tool may be used during the planning phase and implementation phase of stormwater program Pollutants are user-defined
• The user may use event mean concentrations (EMCs) directly though additional parameterization is available to reflect other processes such as decay coefficient, the buildup function, washoff function
• This tool is free and available to the public

• There is an optional add-in tool, SWMM Climate Adjustment Tool, which allows future climate projections to be incorporated into the model
• The tool has a very detailed drainage system modeling capability, which includes both stormwater and sewer systems
• The tool offers different options for the equations it uses for its calculations, i.e. Horton’s
• Method, Green-Ampt Method, Curve Number Method, etc. for modeling infiltration
• This tool may be used to support Reasonable Assurance Analysis (RAA)