<br />~ mountains generally are thin and poorly developed and
<br />o primarily are a product of physical weathering of rocks ,
<br />W Soils in the Colorado Plateau are thicker and are
<br />fonned on deposits of recent geologic age, Suspended
<br />sediment in the basin predominantly is a result of
<br />channel erosion and soil erosion from overland flow,
<br />Generally, suspended-sediment concentrations
<br />increase from the eastern edge of the Colorado Plateau
<br />physiographic province to the outflow of the basin at
<br />the Colorado-Utah State line, Suspended-sediment
<br />concentrations are smallest during base-flow condi-
<br />tions and largest during spring runoff when streamflow
<br />discharges are large and sediment is available, Soils in
<br />the agricultural areas of the basin contain soluble salts
<br />that could greatly affect the concentrations of sodium
<br />and calcium in the surface and ground water,
<br />
<br />Human Factors
<br />
<br />Human factors can adversely affect water quality
<br />a~ a result of point and nonpoint sources of chemical
<br />constituents, Because the economy of the mountainous
<br />region depends on outdoor recreation and water-based
<br />activities, such as fishing, white-water boating, flat-
<br />water boating, camping, and hiking, this area is a prior-
<br />ity to the State's water-quality program, For example,
<br />State water-quality standards for aquatic life have nol
<br />been met for cadmium, copper, lead, and zinc in
<br />streams downstream from active and abandoned mines
<br />in the headwaters, In addition, many of the shallow,
<br />unconfined aquifers in Colorado have become contam-
<br />inated with nitrates and salinity resulting from agricul-
<br />tural activities (Colorado Depanment of Health, 1992),
<br />Human factors also can improve water quality; for
<br />example, reselVoirs can trap sediments and metals,
<br />resulting in downstream reaches having better water
<br />quality than the upstream reaches,
<br />Human factors can be described according to the
<br />water and land uses discussed earlier in this report,
<br />Interbasin water transfers, mining, urbanization, and
<br />agriculture are the principal activities that affect water
<br />quality in the basin, In the Upper Colorado River
<br />Basin, these activities occur approximately in a down-
<br />stream order, Interbasin water transfers are in the head-
<br />waters, mining is located in the mountainous areas,
<br />urbanization is in the Southern Rocky Mountains and
<br />Colorado Plateau, and agriculture predominantly is in
<br />the valleys of the Colorado Plateau,
<br />Because interbasin water transfers generally are
<br />made near the stream headwaters, the amount of
<br />streamflow diverted can be a substantial part of the
<br />streamflow near these sources; however, the effect
<br />decreases farther downstream as the volume of flow
<br />
<br />increa~es, Diversions from the ba~in account for about
<br />12 percent of the mean annual streamflow at the
<br />Colorado River near the Colorado-Utah State line,
<br />The Alva B, Adanls Tunnel, which diverts the largest
<br />anlOunt of water in the entire study unit, may be the
<br />cause of increases in dissolved-solids concentrations
<br />in the Colorado River near Glenwood Springs
<br />(Liebennann and others, 1989), Although 9,000 tons
<br />of dissolved solids are removed annually from the
<br />Upper Colorado River Basin through the Alva B,
<br />Adams Tunnel, the principal effect of this diversion is
<br />the removal of relatively pure water from the Colorado
<br />River system,
<br />Mining practices have affected water quality in
<br />several parts of the basin, The headwaters of several
<br />tributaries to the Colorado River such as the Blue,
<br />Eagle, Roaring Fork, and Gunnison Rivers drain one of
<br />the primary metal-mining regions in Colorado, A large
<br />number of active and abandoned metal mines exist in
<br />this region, which is referred to as the Colorado
<br />Mineral Belt. Metal-mining activities usually arc in
<br />areas ofhigh precipitation, resulting in a greater risk of
<br />perennial or ephemeral mine drainage as well a~ stonn-
<br />induced mine drainage from mine dumps and tailings,
<br />Streams have been affected by point-source mine
<br />discharge and nonpoint-source runoff from mined
<br />area~ (Wentz, 1974), Concentrations of cadmium,
<br />copper, iron, lead, manganese, mercury, molybdenum,
<br />and zinc exceed State water-quality standards for local-
<br />ized reaches of these streams (Colorado Water Quality
<br />Control Division, 1989), Some reaches in the basin,
<br />such as Red Mountain Creek near Ouray, are affected
<br />by acid mine drainage, Although local reaches of these
<br />streams have been affected, little is known about the
<br />transport of these metals downstream into the larger
<br />tributaries and the Colorado River,
<br />Coal mining in the area can affect water quality
<br />by increases in dissolved solids, particularly sulfate,
<br />and increases in trace-element concentrations, There
<br />are a number of active oil and gas fields and large
<br />deposits of oil shale, primarily in Garfield County,
<br />Although the effects from oil and gas drilling on the
<br />surface and ground water can be considerable locally,
<br />little is known as to the areal extent of the effects from
<br />this activity, Uranium mining was once active in the
<br />basin, and mining and milling wastes pose serious
<br />threat~ to ground water from radionuclide contamina-
<br />tion, High radium concentrations occur in shallow
<br />aquifers in Montrose County in association with
<br />uranium mining and milling operations (Colorado
<br />Deparunent of Health, 1992),
<br />Urbanization has an important effect on the
<br />water quality of the study unit. Population is increas-
<br />ing at a rate of about 10 percent annually in some of the
<br />
<br />IMPUCATIONS OF ENVIRONMENTAL SETTING ON WATER QUAUTV 29
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