National Water-Quality Assessment (NAWQA) Program
Denver information sheet (2 pg PDF, 2.49 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 Denver Metropolitan Area.
Prepared for November 30, 2012 Congressional briefing
Twenty eight sites were selected with drainage basin areas in the Western High Plains ecoregion portion of the basin between about 1.6 to 216 square miles (4.1 to 559 square kilometers) and had minimal natural variability among them. The land use gradient went primarily from grassland 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.
The Denver study area is in Colorado and Wyoming in the Western USA. Major cities include Denver, Boulder, Longmont, and Fort Collins, Colorado, and Cheyenne, Wyoming. Urban areas are concentrated in the transition zone between the Rocky Mountains and the Great Plains, in an area known as the Front Range urban corridor. The population increased 30.4% from 1990 to 2000 and the 2000 population was 2.6 million people for the Denver-Boulder-Greeley Metropolitan Area (U.S. Census Bureau, 2000).
Elevation ranges from 4,806 feet (1,465 meters) in the plains to 8,350 feet (2,545 meters) in study area (U.S. Geological Survey, 2005). The Front Range is in the Western High Plains ecoregion (Omernik, 1987) which generally contains smooth to irregular plains and natural vegetation is blue gramma and buffalo grass. Land use is dominated by rangeland and agriculture.
The climate is semiarid, with mean a annual precipitation of 17 inches (43 centimeters) and a mean annual temperature of 46 degrees Fahrenheit (8.1 degrees Celsius)(Daymet, 2005). Most precipitation on the plains results from rainfall, which occurs between April and September, whereas most precipitation in the mountains results from snowfall in winter.
Perennial flow in streams originating in the Rocky Mountains is primarily from snowmelt runoff. Smaller tributaries in the plains and along the Front Range are often ephemeral and flow during spring and summer thunderstorms. Typical of arid and semiarid urban areas of Western USA, complex networks of canals and pipes move water between different areas of the basin for domestic water supply, agricultural irrigation, and power generation. This complex irrigation canal network was well established by the early 1900's (Eschner and others, 1983). The plains streams support warm-water biological communities.
Sprague, L.A., Zuellig, R.E., and Dupree, J.A., 2006, Effects of urbanization on stream ecosystems in the South Platte River Basin, Colorado and Wyoming, chap. A of Effects of urbanization on stream ecosystems in six metropolitan areas of the United States: U.S. Geological Survey Scientific Investigations Report 2006-5101-A, 139 p.
For more information about the study area — http://co.water.usgs.gov/nawqa/splt/