WinSLAMM (Source Loading And Management Model): An urban area nonpoint source water-quality model for Wisconsin

Science Center Objects

The WinSLAMM model is used to identify sources of pollutants in urban stormwater runoff and to evaluate management alternatives for reducing pollutants. USGS studies provide stormwater flow and pollutant-concentration data for calibrating and verifying WinSLAMM for use in Wisconsin.

Photo of a grass swale alongside a highway

Bioswale and USGS monitoring equipment along a Wisconsin highway.


Wisconsin municipalities are using urban-runoff models to help them prepare stormwater management plans. Planners and engineers use the models to identify the most important sources of pollutants and to quantify the benefits of different management alternatives to reduce pollutants. WinSLAMM, a Windows version of the Source Loading and Management Model (SLAMM), is one of the models recommended for stormwater planning by the Wisconsin Department of Natural Resources (WDNR). 

All watershed models need to be calibrated before they are applied. Large errors in flow and pollutant concentrations can result if the model is not calibrated to locations where it will be used. In most cases the municipalities will not have the resources to collect the necessary flow and pollutant-concentration data. Fortunately, enough stormwater data have been collected to adjust WinSLAMM for use by municipalities in Wisconsin.


The objective of the project is to calibrate and verify the WinSLAMM model with the stormwater flow and pollutant- concentration data available from urban studies conducted in Wisconsin.


The Wisconsin Department of Natural Resources and the U.S. Geological Survey (USGS) have conducted cooperative research studies collecting flow data and pollutant concentrations in urban stormwater runoff. These data are available for individual source-areas and for storm-sewer outlets along with land use and development characteristics, including percent connected imperviousness, for each study area. This information will be used to calibrate and verify WinSLAMM.

There are three steps involved in calibrating WinSLAMM. First, the predicted runoff volumes need to be adjusted to match the values observed at the storm-sewer outlet. Second, the predicted particle solids loads should be adjusted to match, as much as possible, the observed loads at the monitoring location. The last step is to calibrate pollutant loads for suspended sediment, total and dissolved solids, nutrients, metals, and organics. 

Municipalities can select from among a number of different types of proprietary and nonproprietary types of stormwater control practices to achieve the TSS performance standards. To help reduce the uncertainty several nonpoint source monitoring projects have evaluated a variety of source areas and control practices. This information is used by cooperators to make informed water resource decisions.

Nonpoint evaluation monitoring also provides unique and comprehensive datasets that are of interest to the nonpoint research community at large. It is our intent to continuously evolve data collection and analysis techniques, plan for future projects, and maintain a positive relationship with cooperators. Current and future studies include porous pavement, leaf pickup, bioretention, grass swales, filter strips, source area particle size, and bioretention swales. Data from these studies will be included in future updates of WinSLAMM.

This website was developed for the state of Wisconsin's counties, city managers, and engineers to provide them with the appropriate files to run WinSLAMM. Also, this website provides the watershed managers references so that they can make informed decisions. These studies were used to populate WinSLAMM parameter files that followed a procedure of calibrated and validated runoff quantities and qualities in the model.

A view of WinSLAMM model’s Current File Data.

Figure 1. A view of WinSLAMM model’s Current File Data.

Get USGS WinSLAMM parameter files for Wisconsin


The WinSLAMM program is copyright 1997, John Voorhees and Bob Pitt.

For technical help relating to the WinSLAMM model, please contact: Judy Horwatich (USGS) or Bob Pitt, John Voorhees, Caroline Burger, or Doug Joachim at



The authors gratefully acknowledge the many cooperators involved in research studies that are integrated into WinSLAMM model. Support provided by Wisconsin Department of Transportation, Federal Highway Administration, University of Wisconsin-Madison, University of Wisconsin-Extension, U.S. Environmental Protection Agency, National Sanitation Foundation; Cities of Green Bay, Madison, Middleton, Milwaukee, Waukesha, and Marquette (Mich.); Brown, Dane, Milwaukee, and Waukesha Counties; and countless others not included. We also appreciate the guidance on stormwater-control practice provided by AE com (formally Earthtech), Brown and Caldwell, and McMahon Group.

Collaboration by the following people make WinSLAMM a viable model for urban modelers: Robert Pitt, Roger Bannerman, John Voorhees, Caroline Burger, Doug Joachim, Jim Bachhuber, Judy Horwatich, William Selbig, Mary Anne Lowndes, and others.


*Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.


Description of Wisconsin Source Loading and Management Model (WinSLAMM) parameter files

The U.S. Geological Survey (USGS) and the Wisconsin Department of Natural Resources (WDNR) have conducted cooperative research studies to collect flow and pollutant concentrations in urban stormwater runoff. Available data collected from each study area include individual source-areas and storm-sewer outlets, along with land use and development characteristics such as percent connected imperviousness and unconnected pervious, or an associated control practices. Results from studies are in linked into WinSLAMM by modify coding, calibrating and validating model output. See the flow chart and reference list below for more information on the studies that have improved WinSLAMM.

Downloadable files from this website provide users with parameter files for their area of interest and research references so that they can make knowledgeable decisions about their watershed.  The parameter files match conditions experienced in Wisconsin instead of the default values created for other areas in the United States.

The WinSLAMM model resides on two types of software platforms: Version 9.x and Version 10.x that operates in Microsoft Windows. Based the WinSLAMM version they are using, users must select the appropriate parameter files and apply each to the Current File Data menu. Files descriptions described below are as they appear in the Current File Data menu.

Users outside of Wisconsin can use these files or more appropriate regional files that are included in the WinSLAMM program* by PV and Associates.

Get USGS WinSLAMM parameter files for Wisconsin

Parameter files:

  • Rain Files: .ran
  • Pollutant Probability Distribution File: .ppd or ppdx
  • Runoff Coefficient File: .rsv or .rsvx
  • Particulate Solids Concentration File: .psc or pscx
  • Street Delivery Parameter File: .std
  • Particulate Residue Reduction File: .ppr
  • Particle size distribution file: .cpz or .csv


Rain files (.ran):

The rainfall files created by the USGS are a result of data analysis of historical rainfall records from 1949 to 2008 from the National Weather Service. The periods selected were based on long-term average conditions that represent the average annual rainfall and average five year rainfall. The average five year period may not include the average annual rainfall if an extreme rainfall year occurred before or after that year. Users should choose a reprehensive rainfall file for your area of interest.

Rainfall files of 10, 20, and 30 years are also included in the rainfall file downloads. These long-term rainfall files can help the user determine the longevity of a stormwater treatment device. The rainfall files are also based on the average annual 10, 20, or 30 years rainfall. These rainfall files were also generated from the same set of National Weather Service files.

Final installation of permeable pavement study test plots

Test plots for permeable pavers (foreground), permeable concrete (midground), and permeable asphalt (background).

Post Construction

For post-construction stormwater management, s. NR 151.12, Wis. Adm. Code requires that the performance standards be met on an average annual basis.  Five locations in the state have been selected and their representative rainfall year is identified in s.  NR 151.12(1)(b). When running a model to assess the stormwater control program effectiveness in meeting the post-construction performance standards, the following files must be used.  Select the rainfall file for the location closest year modeling site. 

Five areas for average annual rainfall and dates used in WDNR NR151 Non-Agricultural Performance Standards listed in the table below.

Developed Areas-Street Cleaning

For developed urban areas under s. NR 151.13, permitted municipalities must reduce the TSS load by 20% in 2008 and 40% in 2013. These reductions are reported on an average annual basis. However, there are no identified rainfall years for the developed urban area performance standards in NR 151.13. Since a single year did not fairly represent the impact of street cleaning, a series of rainfall files of 5 consecutive years are required. Use the file closest to your site location listed in the table below.

Permeable Pavement

When modeling permeable pavement it is recommended to use the average annual 20 years of rainfall record. Use the file closest to your site location listed in the table below.

These and other long term rainfall files are available on this website which include 1, 5, 10, 20, 60 years. Rainfall files are also included with WinSLAMM upgrades located in directory WinSLAMM Files\Rain Files\WI_Multi_ran.

Winter Season Range

The USGS measured street-dirt load from several types of roadways to determine the initial street-dirt loads at the end of winter season. Winter practices for removing snow typically increase the street dirt loads by 5-10 higher than loads on roadways in summer and fall seasons. After the winter season is over the model deposits the winter street-dirt load on the roadway. The amount of winter load is dependent on the street texture and landuse. The street-dirt load is removed through rainfall washoff or street cleaning routines.

Photo of water-quality sampling in a grass swale on a divided highway

Water-quality sampling in a grass swale along a divided highway

Check the winter-season range box to include the range of dates prescribed; typically the winter season is checked if evaluating Wisconsin NR151 rules. The winter ranges are listed in the table below next to the regional rainfalls files. The model run will exclude all rainfall dates in the winter season range. The dates need to be entered using the format "mm/dd".

Pollutant Probability Distribution files (.ppd or .ppdx):

Data from the pollutant probability distribution file are geometric-mean concentration for numerous pollutants. The PPD file is populated with concentration containing each source area for all six landuses. The pollutants concentrations are populated by dissolved concentrations (mg/L) and particulate mass (mg/kg). For each rainfall WinSLAMM computes particulate-sediment loads for those constituents selected by the user. The dissolve load is computed by multiplying the source area concentration by the runoff volume. The particulate load is computed by multiplying the source area mass by the particulate sediment load and runoff volume. A total constituent load adds the dissolved and particulate loads.

Geometric means were computed from several monitored source areas studies. Monitored data collected from source areas include: residential, commercial, and industrial rooftops; residential lawns; residential driveways; residential, commercial and industrial streets; commercial and industrial parking lots; freeways; and undeveloped area. Concentrations included dissolved and total phosphorus, copper, zinc, lead, and cadmium. None of the geometric means were altered in the calibration process. See the table below to choose the correct WI pollutant probability distribution file.

Runoff Coefficient files (.rsv or .rsvx):

WinSLAMM uses small storm hydrology to determine runoff volumes. Instead of using a single runoff curve number for urban areas the model interpolates a curve number based on the source area and rainfall depth. Types of source area in the runoff coefficient file include connected flat roofs, connected pitched roofs, directly connected impervious areas, directly connected unpaved areas, smooth textured streets, intermediate textured streets, and rough textured streets, and high traffic urban.  Pervious areas include sandy (A) soils, silty (B) soils, clayey (C/D) soils, and high traffic urban pervious. Flows measured by the Wisconsin Water Science Center calibrated the runoff coefficient files in the table below

Particulate Solids Concentration files (.psc or .pscx):

Files contain individual source areas concentrations for each of the six landuses. Particulate solids concentrations are multiplied by runoff volumes and a conversion factor, to calculate particulate solids loadings in WinSLAMM. Total suspended solids concentrations were measured by the USGS in runoff from many different source areas per landuse. The source areas data were collected: rooftops from residential, commercial, and industrial; lawns and driveways from residential area; streets from residential, commercial and industrial areas; parking lots from commercial and industrial areas; pervious and impervious high traffic urban from freeway areas; and pervious undeveloped areas. The Wisconsin Water Science Center calibrated the WI particulate solids concentrations files in the table below.

Street Delivery files (.std):

The street delivery file contains the predefined street-textures fractions for total particulate solids not reaching the outfall during individual event. The washoff routine in the model generates an event street load that depends on the current street-dirt load (previous street load plus street dirt accumulation), the rainfall depth, and intensity. The street delivery file has higher fractions for smaller rainfalls because lower volume events usually have less energy to carry particles off the street. There are two files based on landuse type and were introduced in version 8.1. The Wisconsin Water Science Center calibrated the WI street delivery files in the table below.

Particulate Residue Reduction files (.ppr):

WinSLAMM uses the particulate residue reduction subprogram to create parameter files that describe the fraction of total particulates that remains in the drainage system (curbs and gutters, grass swales, and storm drainage) after rain events end due to deposition. This fraction of the total particulates does not reach the outfall, so the outfall values are reduced by the fraction indicated in the .PRR file.  The reduction of particulate residue at the outfall due to the delivery system is a function of the type of drainage system and rainfall depth.  WinSLAMM calculates this deposition effect for three different drainage systems, based on the condition of the curb and gutter. The Wisconsin Water Science Center placed zeros in the Version 9 WI particulate residue reduction file (this file was eliminated in version 10; see table below).

Particle size distribution file (.cpz or .csv):

Particle-size distribution file, also known as critical particle size file, is required to when a management practice is used to determine pollutant removal efficiencies. Practices presently using the particle size file are wet detention ponds, grass swales, filter strips, porous pavement, biofilters, hydrodynamic devices, and catch basin in version 10.1 and earlier. In version 10.2 there is a particle size matrix based on source area and land use. Wisconsin users are to use file in the table below.