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<br />. <br /> <br />Table 4,3. - Flow recommendations for the Colorado River; measured at the USGS <br />gage near Cisco, Utah (09180500). <br /> <br />. <br /> <br />Hydrologic Magnitude' <br />Category (cfs) Discussion/Anticipated Effect <br /> Spring Peak <br />Dry; 212,000 Only limited in-channel scouring of gravel or cobble bars is anticipated <br />90-100% (> 10,800) at this level. Initial motion is reached or exceeded in only 6% of the <br />exceedance Colorado River and bankfull flow is not reached anywhere. No flooded <br /> bottomlands will be provided, but some inundation of tnbutary mouths <br /> will occur. The small peak will provide spawning cues for Colorado <br /> pikeminnow, razorback sucker, and humpback chub. <br />Moderately Dry; > 20,000 Initial motion is reached or exceeded in 60% of the Colorado River at <br />70-90% (> 18,000) this level, so considerable in-channel scouring of gravel and cobble <br />exceedance . bars will occur. Clean gravel and cobble will be available for egg <br /> deposition and invertebrate production in wide areas of the river. <br /> Bankfull flow is reached in only 5% of the river so maintenance of side <br /> channels, etc will be limited. Floodplain inundation will be small and <br /> brief, but will provide some warm quiet-water habitats for growth and <br /> gonad maturation of endangered fish. The backwater at Walker SW A <br /> will provide some of this quiet habitat. <br />Average-Dry; >27,000 Initial motion is reached or exceeded in 91 % of the river so in-chartnel <br />50- 70% (224,300) scouring of gravel and cobble bars will be wide spread. Wide spread <br />exceedance areas with clean substrates for egg deposition and incubation should <br /> provide habitat needed for maximum reproductive success of Colorado <br /> pikeminnow, razorback sucker, and humpback chub, and increased <br /> primary and secondary production. Bankfull flow is reached or <br /> exceeded in 7% of the Colorado River, so maintenance of major habitat <br /> features within the channel will be limited. Floodplain inundation will <br /> increase, but will be limited in duration; however, warm, quiet-water <br /> habitats will be available early in the year for growth and gonad <br /> maturation of razorback sucker and Colorado pikeminnow. <br />A verage- Wet; >35,000 Initial motion is reached or exceeded in 98% of the river and bankfull <br />30-50% (>31,500) flow is reached or exceeded in about 25%. In-channel habitats used by <br />exceedance endangered fish will be maintained in important river reaches; channel <br /> narrowing will be slowed or prevented. Flooding in and around Walker <br /> SW A will provide important floodplain habitats, but the extent of <br /> available habitat is not known. Widespread areas with clean substrate <br /> should provide habitat needed for maximum reproductive success of <br /> Colorado pikeminnow, razorback sucker and humpback chub, and <br /> increased primary and secondary production. <br />Moderately Wet; 243,000 Initial motion is reached or exceeded in 100% of the river and bankfull <br />10-30% (238,700) flow is reached or exceeded in about 42% of the river, creating and <br />exceedance maintaining important habitats for Colorado pikeminnow and <br /> razorback sucker in wide areas of the river. Floodplain habitats will be <br /> extensive, but the surface area of those habitats is not quantified Flows <br /> should exceed 35,000 cfs for at least 2 weeks to maximiie the <br /> availability of floodplains habitats to young-of-year razorback sucker. <br /> <br />. <br /> <br />Draft Final Report <br />May 30, 2000 <br /> <br />Chapter 4 <br /> <br />4-22 <br /> <br />- <br /> <br />f <br /> <br />( <br />