Environmental Setting and Implications on Water Quality,
<br />Upper Colorado River Basin, Colorado and Utah
<br />By Lori E. Apodaca, Nancy E. Driver, Verlin C. Stephens, and Norman E. Spahr
<br />Abstract
<br />The Upper Colorado River Basin in
<br />Colorado and Utah is 1 of 60 study units selected
<br />for water-quality assessment as part of the
<br />U.S. Geological Survey's National Water-Quality
<br />Assessment program, which began full implemen-
<br />tation in 1991. Understanding the environmental
<br />setting of the Upper Colorado River Basin study
<br />unit is important in evaluating water-quality issues
<br />in the basin. Natural and human factors that affect
<br />water quality in the basin are presented, including
<br />an overview of the physiography, climatic condi-
<br />tions, general geology and soils, ecoregions,
<br />population, land use, water management and use,
<br />hydrologic characteristics, and to the extent
<br />possible aquatic biology. These factors have sub-
<br />stantial implications on water-quality conditions
<br />in the basin. For example, high concentrations of
<br />dissolved solids and selenium are present in the
<br />natural background water conditions of surface
<br />and ground water in parts of the basin. In addition,
<br />mining, urban, and agricultural land and water
<br />uses result in the presence of certain constituents
<br />in the surface and ground water of the basin that
<br />can detrimentally affect water quality. The envi-
<br />ronmental setting of the study unit provides a
<br />framework of the basin characteristics, which is
<br />important in the design of integrated studies of
<br />surface water, ground water, and biology.
<br />60 study units representing the Nation's most important
<br />river basins and aquifers are being investigated.
<br />Information obtained from the different study units will
<br />help in the management, regulatory, and monitoring
<br />decisions by other Federal, State, and local agencies to
<br />better protect, use, and enhance water resources. To
<br />effectively design and conduct a multidisciplinary
<br />water-quality assessment of a large basin, the current
<br />environmental setting and implications on water
<br />quality need to be determined.
<br />The Upper Colorado River Basin study unit
<br />(fig. 1) in Colorado and Utah has a drainage area of
<br />about 17,800 miz; all except 100 mil of this area is in
<br />Colorado (Driver, 1994). The Colorado River and its
<br />tributaries originate in the mountains of central
<br />Colorado and flow about 230 mi southwest into Utah.
<br />These mountains form the Continental Divide, which is
<br />the eastern and southern boundary of the study unit.
<br />The major tributaries to the Colorado River in the study
<br />unit are the Blue, Eagle, Roaring Fork, and Gunnison
<br />Rivers.
<br />The study unit is predominantly rural and has a
<br />population of about 234,000 people (Bureau of Census,
<br />1990), with more than 99 percent of the people residing
<br />in Colorado. The largest population center in the basin
<br />is the area around Grand Junction, Colo. Tourism is a
<br />major year-round activity and accounts for substantial
<br />increases in population primarily during the winter and
<br />summer (Driver, 1994).
<br />Purpose and Scope
<br />INTRODUCTION
<br />In 1991, the U.S. Geological Survey,
<br />U.S. Department of the Interior, began full implemen-
<br />tation of the National Water-Quality Assessment
<br />(NAWQA) program. The long-term goals of the
<br />NAWQA program are to: (1) Describe current water-
<br />quality conditions for a large part of the Nation's
<br />freshwater streams, rivers, and aquifers; (2) describe
<br />how water quality is changing over time; and
<br />(3) improve understanding of the primary natural and
<br />human factors that affect water-quality conditions
<br />(Leahy and others, 1990). In meeting these goals,
<br />This report describes environmental characteris-
<br />tics of the Upper Colorado River Basin study unit and
<br />the natural and human factors that are considered to
<br />affect current (1995) water-quality conditions in the
<br />basin. The description of the environmental setting is
<br />based on a review of data and reports from Federal,
<br />State, and local agencies and industries. For more
<br />information on environmental characteristics and
<br />water-quality conditions and issues in the study unit,
<br />the reader can refer to a bibliography ofwater-related
<br />studies within the Upper Colorado River Basin (Bauch
<br />and Apodaca, 1995) or to specific literature cited in this
<br />report.
<br />Abstract
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