National Water-Quality Assessment (NAWQA) Program
Atlanta information sheet (2 pg PDF, 4.12 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 Atlanta Metropolitan Area.
Prepared for November 30, 2012 Congressional briefing
Thirty sites were selected with drainage basin areas between 17 to 56 square miles (43 to 146 square kilometers) and 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 fall 2002 to summer 2003.
The Atlanta study area is in Georgia and parts of Alabama in the southeastern USA. The population has increased 38.9% from 1990 to 2000 and was about 4.1 million people in 2000 (U.S. Census Bureau, 2000). The study area is in the Piedmont ecoregion (Level III, USEPA, 2000), and includes the Southern Inner and the Southern Outer Piedmont (Level IV; Griffith and Omernik, 1999) sub-provinces, portions of which are located in both Georgia and Alabama.
The Piedmont ecoregion is characterized by gently rolling topography with approximately 200 feet (61 meters) of local relief and dissected irregular plains; streams are typified by low to moderate gradients and as having cobble, gravel, and sandy substrates. Elevation in the study area ranges from about 328 to 1526 feet (100 to 465 meters) above sea level (U.S. Geological Survey, 2005).
Potential natural vegetation in the Piedmont ecoregion is oak-hickory-pine forest, however, current land use and land cover includes forested areas in silviculture as well as agricultural production of hay, cattle, and poultry (Griffith and Omernik, 1999, U.S. Geological Survey, 2001). 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 (Trimble, 1969).
The climate is warm and humid with mean annual temperature of 62 degrees Fahrenheit (16.6 degrees Celsius) and mean annual rainfall of 52 inches (131 centimeters), evenly distributed throughout the year, except for a dry period in August to October (Daymet, 2005).
Streamflow in the southern Piedmont is generally highest in the winter when rainfall is primarily derived from slow-moving frontal systems and lowest in late summer and fall when fast-moving thunderstorms are more prevalent. Streams in this region support diverse warm-water biological communities.
Gregory, M.B., and Calhoun, D.L., 2007, Physical, Chemical, and Biological Responses of Streams to Increasing Watershed Urbanization in the Piedmont Ecoregion of Georgia and Alabama, 2003, U.S. Geological Survey Scientific Investigations Report 2006-5101-B.
For more information about the study area — http://ga.water.usgs.gov/nawqa/index.html