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<br />~Environmental Setting and Implications on Water Quality,
<br />o Upper Colorado River Basin, Colorado and Utah
<br />
<br />By Lori E. Apodaca, Nancy E, Driver, Verlin C, Stephens, and Norman E. Spahr
<br />
<br />Abstract
<br />
<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 characteIistics, and to the extent
<br />possible aquatic biology, These factors havc 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 pans of the basin, In addition,
<br />mining, urban, and agricultural land and water
<br />uses result in the presence of cel1ain 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 />impol1ant in the design of integrated studies of
<br />surface water. ground water, and biology,
<br />
<br />INTRODUCTION
<br />
<br />In 1991, the U,S, Geological SUlvey,
<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 />NA WQA program are to: (I) 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 />
<br />60 study units representing the Nation's most important
<br />river ba~ins and aquifers are being investigated,
<br />Information obtained from the different study unit~ 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 ba~in, 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, I) in Colorado and Utah ha~ a drainage area of
<br />about 17,800 mi'; all except 100 mi' of this area is in
<br />Colorado (Driver, 1994), The Colorado River and its
<br />tributaries originate in the mountains of central
<br />Colorddo and flow about 230 mi southwest into Utah,
<br />These mountains foml 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 activ ity and accounts for substantial
<br />increases in population primarily during the winter and
<br />summer (Driver, 1994),
<br />
<br />Purpose and Scope
<br />
<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 currcnt (1995) water-quality conditions in the
<br />ba~in, 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 />infornlation on environmental characteristics and
<br />water-quality conditions and issues in the study unit,
<br />the reader can refer to a bibliography of water-related
<br />studies within the Upper Colorado River Ba~in (Bauch
<br />and Apodaca, 1995) orto specific literature cited in this
<br />report,
<br />
<br />Abstract 1
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