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Scientific Investigations Report 2012–5070

National Water-Quality Assessment Program

Representation of Regional Urban Development Conditions Using a Watershed-Based Gradient Study Design

By Silvia Terziotti, Gerard McMahon, and Amanda H. Bell


As part of the U.S. Geological Survey National Water-Quality Assessment Program, the effects of urbanization on stream ecosystems (EUSE) have been intensively investigated in nine metropolitan areas in the United States, including Boston, Massachusetts; Atlanta, Georgia; Birmingham, Alabama; Raleigh, North Carolina; Salt Lake City, Utah; Denver, Colorado; Dallas–Fort Worth, Texas; Portland, Oregon; and Milwaukee–Green Bay, Wisconsin. Each of the EUSE study area watersheds was associated with one ecological region of the United States. This report evaluates whether each metropolitan area can be generalized across the ecological regions (ecoregions) within which the EUSE study watersheds are located. Seven characteristics of the EUSE watersheds that affect stream ecosystems were examined to determine the similarities in the same seven characteristics of the watersheds in the entire ecoregion. Land cover (percentage developed, forest and shrubland, and herbaceous and cultivated classes), average annual temperature, average annual precipitation, average surface elevation, and average percentage slope were selected as human-influenced, climate, and topography characteristics. Three findings emerged from this comparison that have implications for the use of EUSE data in models used to predict stream ecosystem condition. One is that the predominant or "background" land-cover type (either forested or agricultural land) in each ecoregion also is the predominant land-cover type within the associated EUSE study watersheds. The second finding is that in all EUSE study areas, the watersheds account for the range of developed land conditions that exist in the corresponding ecoregion watersheds. However, six of the nine EUSE study area watersheds have significantly different distributions of developed land from the ecoregion watersheds. Finally, in seven of the nine EUSE/ecoregion comparisons, the distributions of the values of climate variables in the EUSE watersheds are different from the distributions for watersheds in the corresponding ecoregions.

Revised August 29, 2012

First posted May 24, 2012

For additional information contact:
USGS North Carolina Water Science Center
3916 Sunset Ridge Road
Raleigh, NC 27607
phone: (919) 571–4000

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Suggested citation:

Terziotti, Silvia, McMahon, Gerard, and Bell, A.H., 2012, Representation of regional urban development conditions using a watershed-based gradient study design: U.S. Geological Survey Scientific Investigations Report 2012–5070, 109 p.





Purpose and Scope


Ecoregion Watershed Delineation

Methods of Comparison



Salt Lake City









Background Land Cover is Either Forested or Agricultural

Representativeness of the EUSE Urban Gradient Relative to the Gradient for the Entire Ecoregion

Climate Zones




Appendix 1—Study watersheds in nine metropolitan areas used in the effects of urbanization on stream ecosystems study

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