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The USGS implemented the National Water-Quality Assessment (NAWQA) Program in 1991 to support national, regional, and local information needs and decisions related to water-quality management and policy. Shaped by and coordinated with ongoing efforts of other Federal, State, and local agencies, the NAWQA Program is designed to answer: What is the condition of our Nation’s streams and ground water? How are the conditions changing over time? How do natural features and human activities affect the quality of streams and groundwater, and where are those effects most pronounced? By combining information on water chemistry, physical characteristics, stream habitat, and aquatic life, the NAWQA Program aims to provide science-based insights for current and emerging water issues and priorities.
The Upper Colorado River Basin is one of 51 water-quality assessments initiated since 1991, when the U.S. Congress appropriated funds for the USGS to begin the NAWQA Program.
USGS Circular 1214 summarizes major findings about water quality in the Upper Colorado River Basin that emerged from an assessment conducted between 1996 and 1998.
The Upper Colorado River Basin in Colorado and Utah has a drainage area of about 17,800 square miles, all except 100 mi² of this area is in Colorado (Driver, 1994). The Colorado River and its tributaries originate in the mountains of central Colorado and flow about 230 mi southwest into Utah. The Continental Divide marks the eastern and southern boundary of the basin, with altitudes over 14,000 ft. Topography in the western part of the basin generally consists of high plateaus bordered by steep cliffs along the valleys, and the lowest altitude (4,300 ft) is near the Colorado-Utah border. The basin is divided almost equally into two physiographic provinces: the Southern Rocky Mountains in the eastern part and the Colorado Plateau in the western part (Hunt, 1974). The geology varies substantially and consists of crystalline rocks of Precambrian age, stratified sedimentary rocks, and alluvial deposits.
Because of large changes in altitude, the climate in the basin varies substantially from alpine conditions in the east to semiarid in the west. Mean annual temperatures range from as low as 32.8° F in Gunnison County near the Continental Divide to as high as 54.1° F near Grand Junction, Colo. (Benci and McKee, 1977).
Precipitation in the basin ranges from more than 40 in./yr in the eastern mountainous regions to less than 10 in./yr in the lower altitude western regions. Mountain areas receive most of their precipitation during the winter months when accumulation of snow can exceed on average 100 in. per season. The Grand Junction area receives the largest amount of precipitation during the month of August as a result of weather patterns that produce late-afternoon thunderstorms (Chaney and others, 1987).
The 1990 population in the largely rural Upper Colorado River Basin was approximately 234,000, less than 10 percent of the total population of the State of Colorado (Bureau of Census, 1990). The largest population center is Grand Junction (30,209), which is located at the confluence of the Colorado and Gunnison Rivers. The larger cities in the basin are located predominantly near agricultural lands or in mountain recreational communities. Population of many counties in the basin increased about 5 percent from 1990 to 1992. Eagle and Summit Counties had the largest increases, of about 12 and 13 percent, respectively.
Land designated for use as either rangeland or forest is the largest land use, accounting for about 85 percent of the basin. Large parts of the study unit are set aside for recreational use, including all or parts of 4 National Park Service areas, 5 National Forests and numerous wilderness areas, 11 State parks, numerous State Wildlife Management areas, and 17 ski areas. Tourism and recreational activities are a major industry in the study unit past and present. Mining activities past and present are an important land use and have included the extraction of metals and energy fuels. Urban land is one of the smaller land uses in the mostly rural basin. Agriculture is the traditional land use in the study unit in counties such as Delta, Garfield, Gunnison, Mesa, and Montrose. Little crop production is possible without irrigation because of the semiarid climate.
The NAWQA Program was not intended to assess the quality of the Nation’s drinking water, such as by monitoring water from household taps. Rather, the assessments focus on the quality of the resource itself, thereby complementing many ongoing Federal, State, and local drinking-water monitoring programs. The comparisons made in this study to drinking-water standards and guidelines are only in the context of the available untreated resource.
Water-quality conditions in the Upper Colorado River Basin are a result of both natural and human factors.
Below are other science projects associated with this project.
Below are publications associated with this project.