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Open-File Report 2011–1052

In cooperation with the Wisconsin Department of Natural Resources

Characterizing the Size Distribution of Particles in Urban Stormwater by Use of Fixed-Point Sample-Collection Methods

By William R. Selbig and Roger T. Bannerman


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The U.S Geological Survey, in cooperation with the Wisconsin Department of Natural Resources (WDNR) and in collaboration with the Root River Municipal Stormwater Permit Group monitored eight urban source areas representing six types of source areas in or near Madison, Wis. in an effort to improve characterization of particle-size distributions in urban stormwater by use of fixed-point sample collection methods. The types of source areas were parking lot, feeder street, collector street, arterial street, rooftop, and mixed use. This information can then be used by environmental managers and engineers when selecting the most appropriate control devices for the removal of solids from urban stormwater.

Mixed-use and parking-lot study areas had the lowest median particle sizes (42 and 54 µm, respectively), followed by the collector street study area (70 µm). Both arterial street and institutional roof study areas had similar median particle sizes of approximately 95 µm. Finally, the feeder street study area showed the largest median particle size of nearly 200 µm. Median particle sizes measured as part of this study were somewhat comparable to those reported in previous studies from similar source areas. The majority of particle mass in four out of six source areas was silt and clay particles that are less than 32 µm in size.

Distributions of particles ranging from <2 to >500 µm were highly variable both within and between source areas. Results of this study suggest substantial variability in data can inhibit the development of a single particle-size distribution that is representative of stormwater runoff generated from a single source area or land use. Continued development of improved sample collection methods, such as the depth-integrated sample arm, may reduce variability in particle-size distributions by mitigating the effect of sediment bias inherent with a fixed-point sampler.

Posted April 2011

For additional information contact:
Director, Wisconsin Water Science Center
U.S. Geological Survey
8505 Research Way
Middleton, Wisconsin 53562

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Suggested citation:

Selbig, W.R., and Bannerman, R.T., 2011, Characterizing the size distribution of particles in urban stormwater by use of fixed-point sample-collection methods: U.S. Geological Survey Open-File Report 2011–1052, 14 p.




Description of Source Study Areas


Characterizations of Particle-Size Distributions

Limitations and Suggestions for Further Research

Summary and Conclusions


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