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<br />Oand birds, The Uncompahgre Project area is a major
<br />00 source of selenium to the Gunnison River, and the
<br />o effects of selenium on the endangered fish and birds
<br />~ in this area are not known (Butler and others, 1991),
<br />The presence of other trace elements in the water
<br />supply can result from irrigation, This is due to rcuse
<br />of irrigation water and leaching of naturally occurring
<br />trace elements from the soils,
<br />
<br />SUMMARY
<br />
<br />The goals of the U,S, Geological Survey's
<br />NA WQA program are to describe current conditions
<br />for a large part of the Nation's surface- and ground-
<br />water ,resources, describe how water quality is
<br />changmg over time, and identifY the major natural and
<br />human factors that affect the water quality, The Upper
<br />Colorado River Basin study is I of60 study unit~
<br />selected for water-quality assessment. Information
<br />about the environmental setting provides a framework
<br />of the basin characteristics and includes natural and
<br />human factors that affect the physical, chemical, and
<br />biological quality of the water in the basin, This infor-
<br />mation can be used to design data-collcction studies in
<br />the study unit for the NAWQA program and can aid in
<br />determining the effects of natuml conditions and
<br />human factors on water quality in the basin,
<br />The study unit has a drainage area of about
<br />17,800 mi', and the primary river within the basin, the
<br />Colorado River, originates in the mountains of central
<br />Colorado and flows about 230 mi southwest into Utah,
<br />The major tributaries to the Colorado River in the study
<br />unit are the Blue, Eagle, Roaring Fork, and Gunnison
<br />Rivers, In 1990, population in the basin was about
<br />234,000, The largest population center in the basin is
<br />in the area around Grand Junction,
<br />Climate in the basin varies from alpine condi-
<br />tions in the ea~tern part to semiarid in thc western part.
<br />Mean annual precipitation ranges from more than
<br />40 in, at the higher altitudes to less than lOin, in the
<br />lower altitudes of the basin, The geology predomi-
<br />nantly consists of crystalline rocks of Precambrian age,
<br />stratified sedimentary rocks, and alluvial deposits,
<br />Land designated for use a~ rangeland or forest
<br />accounts for about 85 percent of the use in the basin,
<br />The other major land uses in the basin are agriculture,
<br />mining, and urban, Water used from surface water
<br />for irrigation account~ for about 97 percent of the total
<br />offstream water use, Ground water, which accounts for
<br />less than I percent of water used, typically is used for
<br />domestic purposes in the rural parts of the basin,
<br />Study unit streams are classified in this report
<br />into three general types: high-altitude streams, low-
<br />altitude streams, and mixed-type streams, Annual,
<br />
<br />seasonal, flood, and low flows in these three stream
<br />types vary considerably in the basin, The natural
<br />hydrology has been extensively altered by water devel-
<br />opmen~ which includes numerous reselVoirs and
<br />diversions,
<br />
<br />In the study unit, ground-water resources have
<br />not been extensively developed, The most productive
<br />wells come from alluvial aquifers in the basin, Other
<br />ground-water resources include consolidated aquifer
<br />systems in sedimentary rocks and fractured systems
<br />such as those in metamorphic and granilic rocks,
<br />
<br />Algae, fish, and macroinvertebrates that are
<br />characteristic of the Southern Rocky Mountains and
<br />Colorado Plaleau physiographic provinces vary wilh
<br />altitude and physical habitat. The dominant algae in
<br />Ihe high-altitude streams are blue-green and green
<br />algae, In the lower altitudes, golden-brown and green
<br />algae are predominant. Cold water species, such as
<br />trout, are present at the higher altitudes, and warm-
<br />water species, such as carp, catfish, minnows, and
<br />suckers, dominate the lower altitudes, In Ihe higher
<br />allitudes, caddisflies and mayflies are the dominant
<br />macroinvenebrates, The lower altitudes are favorable
<br />to species such as leeches and snails,
<br />
<br />Natural and human factors affect the physical,
<br />chemical, and biological characteristics in the basin,
<br />which then affect the water quality, The natural weath,
<br />ering processes ofa variety of geologic formations in
<br />the basin add salts, minerals, radionuclides, and trace
<br />elements to the surface and ground waters, Interbasin
<br />water transfers along the Continental Div ide decrease
<br />the quantity of water in the headwater streams and the
<br />di lution capability of these streams, Water quality in
<br />the headwater streams along the Colorado Mineral Belt
<br />is being degraded by past mining activities that affecl
<br />aquatic life, Urbanization and recreational activities
<br />are increasing throughout the basin and have a marked
<br />effect on the quantity ofwatcr needed a~ well a~ the
<br />quality, In the lower part of the basin, agriculture has a
<br />major effect on the quality of surface and ground
<br />waters predominantly because of return flows from irri,
<br />gation,
<br />
<br />REFERENCES CITED
<br />
<br />Ackerman, DJ" and Brooks, Tom, 1986, Recnnnaissance
<br />of ground-water resources in the North Fork Gunnison
<br />River Basin, southwestern Colorado: V,S, Geological
<br />Survey Water-Resources Investigations Report
<br />85-4230,21 p,
<br />
<br />Apley, Martyn. 1982, Powderhorn surface water quality
<br />Sludy; Gunnison, Colorauo Western State College,
<br />46p,
<br />
<br />SUMMARY 31
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