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<br />ATIACIIMENT #1 22C
<br />
<br />Table 4.2. - Flow recommendations for the Gunnison River; measured at the
<br />USGS gage near Grand Junction, Colorado (09152500).
<br />
<br />Hydrologic Magnitude'
<br />Category (cfs) Discussion! Anticipated Effect
<br /> Spring Peak, Mean Daily Flow
<br />Dry; ,4,000 No in-channel scouring of gravel or cobble bars is anticipated at this
<br />90. I 00% (,3,600) flow; however, fine material on the surface will be moved and further
<br />exceedance deposition will be slowed, No flooded bottomland habitats will be
<br /> provided, but some inundation of tributary mouths will occur. The
<br /> small peak will provide spawning cues for Colorado pikeminnow and
<br /> razorback sucker.
<br />Moderately Dry; ,7,000 Limited in-channel maintenance will occur; initial motion is reached or
<br />70-90% (,6,300) exceeded in about 33% of the river, providing clean cobble-gravel
<br />exceedance substrates for egg deposition and invertebrate production in parts ofthe
<br /> river, The limited peak will provide spawning cues for Colorado
<br /> pikeminnow and razorback sucker, Floodplain inundation will be small
<br /> and very brief, but will provide some warm, quiet water habitats for
<br /> growth and gonad maturation of endangered fIsh,
<br />Average-Dry; ,9,500 Initial motion is r~ached or exceeded in 75% of the river, providing
<br />50- 70% (,8,500) wide-spread cleansing of gravel and cobble bars, Bankfull flow is
<br />exceedance reached or exceeded in about 7% of the river, providing some in-
<br /> channel maintenance of important habitats used by endangered fish in
<br /> other seasons, Wide-spread areas with clean substrates for egg
<br /> deposition and in<::ubation should provide for maximum reproductive
<br /> success of Colorado pikeminnow and increased primary and secondary
<br /> production, Floodplain inundation will increase, but will be limited in
<br /> duration; however, some warm, quiet-water habitats will be available
<br /> for growth and gonad maturation of razorback sucker and Colorado
<br /> pikeminnow.
<br />A verage- Wet; ,12,500 Initial motion is reached or exceeded in 100% of the river and bankfull
<br />30-50% (>11,300) flow is reached or exceeded in about 33%, In-channel habitats used by
<br />exceedance endangered fish will be maintained in important river teaches; channel
<br /> narrowing will be slowed or prevented, Floodplain habitats will be
<br /> widespread (about 180 ac will be available at Escalante SWA), but
<br /> duration of flooding will be brief. Quiet water habitats will be
<br /> available for use of adult endangered fish, but flooding duration will be
<br /> limited, Wide-spread areas with clean substrates should provide habitat
<br /> needed for maximum reproductive success of Colorado pikeminnow
<br /> and increased primary and secondary production.
<br />Moderately Wet; ~ 16,000 Bankfull flow is reached or exceeded in 70% of the rivet, creating and
<br />10-30% (,14,400) maintaining important habitats for Colorado pikeminnow and
<br />exceedance razorback sucker in large areas of the river. Gravel is flushed from
<br /> pools, creating important winteting habitat for both species,
<br /> Floodplains are extensive (about 260 ac at Escalante SW A at 16,000
<br /> cfs); river flows should exceed 12,500 cfs (providing 180 ac of habitat)
<br /> for at least 2 weeks to provide floodplain habitat for growth and
<br /> survival of larval razorback sucker.
<br />
<br />Draf: Final Report
<br />May 30, 2000
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<br />4-13
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<br />Chapter 4
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