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Effects of Urbanization on Stream Ecosystems

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Stream with low level of urban intensity.


Stream with moderate level of urban intensity.


Stream with high level of urban intensity.

Raleigh, North Carolina

Raleigh information sheet (2 pg PDF, 2.8 Mb)

This information sheet highlights selected findings of a comprehensive assessment by the National Water-Quality Assessment Program of the U.S. Geological Survey of the effects of urban development on stream ecosystems in nine metropolitan study areas. These are a few of the findings from the study in the Raleigh Metropolitan Area.

Prepared for November 30, 2012 Congressional briefing

Study design:

Thirty sites were selected with drainage basin areas between about 2 to 32 square miles (5 to 82 square kilometers) and had minimal natural variability among them. The land use gradient went primarily from forest to urban. Sites represented a broad range of urban intensity from low to high.

Landcover, urban intensity, and site locations

Time of study:

Site selection in 2002.
Data collection from summer 2002 to fall 2003.

General Description:

The Raleigh study area is in North Carolina in the southeastern USA. Major cities are Raleigh, Durham, Cary, Greensboro, Winston-Salem, and High Point, located along the interstate-40 corridor. The 2000 population in the Raleigh-Durham-Chapel Hill Census Metropolitan Area was 1.2 million, a 38.% increase from 1990 Census and in the Greensboro-Winton-Salem-High Point Metropolitan Area was 1.3 million, a 19.2% increase from 1990 (U.S. Census Bureau, 2000).

The study area is in the Piedmont ecoregion (Omernik, 1987), specifically in three sub-ecoregions: Northern Outer Piedmont, Southern Outer Piedmont, and Carolina Slate Belt. Landforms in all of these regions are irregular plains with some hills (Griffith and others, 2002).

Land use of the area has undergone major transformations from oak-hickory-pine forest to agricultural lands, back to forest, and now to urban and suburban lands. At one time, the region was heavily farmed for cotton, tobacco, corn and wheat and many areas suffered moderate to severe erosion of the silt/clay soils (Trimble, 1974) that are characteristic of the region.

Elevation ranges from about 164 to 1,033 feet (50 to 315 meters) above sea level (U.S. Geological Survey, 2005) The climate is warm and humid with mean annual temperature of 59 degrees Fahrenheit (15 degrees Celsius) and mean annual rainfall of 46 inches (118 centimeter) (Daymet, 2005). Rainfall is evenly distributed throughout the year, with slightly more rainfall in July and August and slightly less in October through December.

Streams have low to moderate gradients and typically have gravel to cobble substrate. Streamflow is highest in the winter months and lowest in late summer. The year prior to sampling (2001-2002) was a period of low rainfall and drought conditions, but rainfall resumed beginning in October 2002. Streams in this region support warm-water biological communities.

Featured Publication:

Giddings, E.M., Moorman, M., Cuffney, T.F., McMahon, Gerard, and Harned, D.A., 2007, Selected physical, chemical, and biological data for 30 urbanizing streams in the North Carolina Piedmont ecoregion, 20022003: U.S. Geological Survey Data Series 279, 14 p.

For more information about the study area —

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