WinSLAMM: The Watershed Runoff Model

The model selected to project pollutant loading in stormwater runoff and for evaluating the selected stormwater BMPs is called Win SLAMM. The model was originally developed to better understand the relationships between sources of urban runoff pollutants and runoff quality when results gained from existing drainage based models did not match actual field measurements.

WinSLAMM offered the DuPage River Watershed Plan a number of advantages:

• An emphasis on small storm hydrology and particulate runoff rather than being centered on analysis of very large and rare rainfall events (a feature of drainage models). This was vital because empirical evidence has shown that stormwater quality problems are mostly associated with frequent and relatively small rains.
• Strongly based on actual field observations
• Allows for a wide variety of source area and outfall control practices (BMPs)
• Has the ability to consider many stormwater controls (affecting source areas, drainage systems, and outfalls) together, for a long series of rains
• It has a history of use on North America where it has been shown to accurately predict stormwater flows and pollutant characteristics for a broad range of rains and control practices.

Due the large data inputs needed by WinSLAMM two subwatersheds were selected for analysis, one from the East Branch DuPage River watershed, 22nd Street Tributary (EBTS) (link to East Branch subwatershed breakdown pdf) draining 494 acres and one from the West Branch DuPage River Watershed, Tributary 3 (WBW3), (link to West Branch subwatershed breakdown pdf) draining 884 acres, totaling 1368 acres.

The selected subwatersheds in the East and West Branch watersheds are in red.  East Branch

Model inputs, as seen on Plate B, included detailed land use maps, source area maps, soil types and rainfall data. Detailed mapping using high resolution ortho-imagery supplied by DuPage County Stormwater Management Division was completed for each subwatershed in order to define source area and land use types. In WinSLAMM land use is defined as a zoning category, with land being placed into various subcategories of residential, open space, institutional, commercial and industrial uses. Source areas refer to infrastructural developments such as roads, sidewalks and buildings. Certain other characteristics were also mapped such as the pitch of roof, levels of connection to a storm drain and the condition of road surfaces. The latter were collected during field visits to the target watersheds. Click to see an example of the land use/source area mapping (link to new window with map & legend at bottom of document). The pollution loads from source areas (roads, sidewalks, driveways, turf areas) were generated using empirical data collected by Wisconsin USGS (United States Geological Survey) rather than the default loadings contained in the model. The availability of this data from an area with similar climate and land uses was a great asset to the project.

The diagram depicts the inputs and outputs from the WinSLAMM model. Image is courtesy of WDR.

BMP inputs used in the model (link to WinSLAMM2.doc)
Model Results (link to WinSLAMM3.doc)
Model Recommendations (link to WinSLAMM4.doc)

Follow the links below for more general information about the Win SLAMM model:
Wisconsin USGS page on WinSLAMM inputs
WinSLAMM developer’s homepage

Part of the West Branch land use and source area map over laid on a 2004 ortho- image. Land use categories are presented here using green space divided between residential, commercial, industrial, freeway, large landscaped and undeveloped space. In fact all source areas are similarly divided. Numeric and alphabetic codes on buildings signify pitched (1) or non-pitched (2), on driveways connected (c) and unconnected (u) and on roads a scale of smoothness (s- smooth, i-intermediate and r –rough). Each source area is coded for these attributes where relevant.