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<br />An examination offlow conditions during
<br />water year 1993 gives a general representation of
<br />water routing along the Colorado River, although flows
<br />during water year \ 993 were above average, Major
<br />interbasin water transfers and reservoirs are shown in
<br />figure 9 and listed in table 3, The Colorado River
<br />below Baker Gulch represents flow in the headwaters,
<br />although the Grand River ditch upstream from Baker
<br />Gulch diverted an annual flow of 71 fi'ls in water year
<br />1993, The Colorado River then flows into Shadow
<br />Mountain ReservoirlLake Granby, from which water
<br />can be diverted through the Alva B. Adams Tunnel.
<br />This complex diversion and storage system was
<br />completed in 1950, Diversions from Grand Lake via
<br />the Alva B. Adanls Tunnel to the South Platte River
<br />Basin are large during all months except June,
<br />
<br />The first major tributary to the Colorado River is
<br />the Blue River, The Harold D, Roberts Tunnel, operat-
<br />ing in conjunction with Dillon Reservoir, has diverted
<br />water from the Blue River Basin since 1963. Annual
<br />flows ofJ08 ft'/s (1993) for the Blue River are affected
<br />by Dillon and Green Mountain Reservoirs, The Eagle
<br />River is the next major tributary adding 542 f\'ls in
<br />water year 1993, Homestake Tunnel and Reservoir
<br />have diverted water from the Eagle River Basin since
<br />1967, In water year 1993, the Colorado River had an
<br />annual flow 01'2,330 ft'/s downstream from the Eaglc
<br />River and 3,970 ft'/s downstream from the Roaring
<br />Fork, which had an annual flow of 1,540 ftl/s in water
<br />year 1993, The Twin Lakes Tunnel (completed in
<br />1935) and the Charles H, Boustead Tunnel (completed
<br />in \972) divert water from the Roaring Fork Basin,
<br />Ruedi Reservoir(completed in 1968) regulates the flow
<br />downstream from the diversions to the Charles H,
<br />Boustead Tunnel. Several small creeks flow into the
<br />Colorado River before it reaches Cameo where it had
<br />an annual flow of4,667 fills in water year 1993,
<br />
<br />The largest tributary to the Colorado River in
<br />Colorado, the Gunnison River, flows into the Colorado
<br />River at Grand Junction, Three small imerbasin water
<br />transfers export water from the Gunnison River head-
<br />waters to the Arkansas and Rio Grande Basins, Three
<br />large dams were built for power generation and water
<br />storage on the main channel of the Gunnison River as
<br />part ofthe Colorado River Storage Project. Together
<br />the reservoirs constitute the Wayne N, Aspinall Unit,
<br />fonnerly known a~ the Curecanti Unit. The largest and
<br />farthest upstream reservoir is Blue Mesa Reservoir;
<br />the others are Morrow Point Reservoir and Crystal
<br />Reservoir, Large volumes of water arc diverted
<br />within the basin thrQugh the Gunnison Tunnel, which
<br />transports water from the Gunnison River to the
<br />Uncompahgre Valley for irrigation (table 3),
<br />
<br />Streamflow in the Uncompahgre River at
<br />Delta is affected by inputs from the Gunnison Tunnel
<br />during April through October and by substantial
<br />evapotranspiration from about 90,000 acres of irrigated
<br />croplands, The annual flow for the Uncompahgre
<br />River in water year 1993 was 387 ftl/s, Ridgway
<br />Reservoir (completed in 1986) is located upstream
<br />from the Uncompahgre River at Delta station and
<br />affects the flow at this station, At the mouth of the
<br />Gunnison River near Grand Junction, the annual flow
<br />wa~ 3,725 ft'/s in water year 1993, The natural flow of
<br />the Gunnison River is affected by diversions for irriga-
<br />tion of about 233,000 acres upstream from this station,
<br />storage reservoirs, and return flow from irrigated
<br />lands, The outflow of the basin, Colorado River near
<br />Colorado-Utah State line, had an annual flow in water
<br />year 1993 of8,491 ft-'/s, of which the Gunnison River
<br />contributed 44 percent.
<br />
<br />Ground Water
<br />
<br />In the study unit, ground-water resources have
<br />not been extensively developed, The most productive
<br />wells come from alluvial aquifers that are fonned from
<br />gravel, landslide, terrace, and glacial deposits in the
<br />basin, Other ground-water resources include consoli-
<br />dated aquifer systems and fractured systems such as
<br />those in metamorphic and granitic rock.~, These aquifer
<br />systems generally yield less water than the unconsoli-
<br />dated aquifers,
<br />Some of the important aquifers in western
<br />Colorado in descending order of age are alluvial,
<br />Green River, Mesaverde, Mancos Shale unit, Dakota,
<br />Morrison, Entrada, Leadville, and Precambrian crystal-
<br />line unit (table 7) (U,S, Geological Survey, 1985), In
<br />some instances, alluvial aquifers might be hydrauli-
<br />cally connected to bedrock aquifers,
<br />
<br />Unconsolidated Aquifers
<br />
<br />Valley-fill alluvial aquifers along the Colorado
<br />River and other perennial streams provide some
<br />water for irrigation, public supply, and industrial use
<br />(U,S, Geological Survey, 1985), Alluvial aquifers in
<br />eroded intennontane valleys are thickest and most
<br />commonly saturated (Ackerman and Brooks, 1986),
<br />Thin aquifers are in alluvium and in eolian deposits on
<br />mesa tops, Aquifers on steep slopes of alluvium, talus,
<br />and colluvium are only seasonally saturated, The
<br />thickness of alluvial aquifers is less than the thic~_ncss
<br />of ait bedrock aquifers in the basin, However, trans-
<br />missivity is much larger in the alluvial aquifers a,
<br />compared to the bedrock aquifers,
<br />
<br />24 Environmental Setting and Implications on Water Quality, Upper Colorado River Baaln, Colorado and Utah
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