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<br />, , <br /> <br />~ <br /> <br />. <br /> <br />. <br /> <br />Table 4.3. - Flow recommendations for the Colorado River; measured at the USGS <br />gage near Cisco, Utah (09180500). <br /> <br />Hydrologic Magnitude <br />Category (cfs) Discussion/Anticipated Effect <br /> Spring Peak <br />Dry; ,12,000 Only limited in-chaMel scouring of gravel or cobble bars is anticipated <br />90-100% at this level. Initial motion is reached in only 6% of the Colorado River <br />exceedence and significant motion is not reached anywhere. No flooded <br /> bottomland habitats will be provided, but some inundation of tributary <br /> mouths will occur. The small peak will provide spawning cues for <br /> Colorado pikerninnow, razorback sucker, and humpback chub. <br />Moderately Dry; ,20,000 Initial motion is reached in 60% of the Colorado River at this level, so <br />70-90% considerable in-channel scouring of gravel and cobble bars will occur. <br />exceedence Clean gravel and cobble will be available for egg deposition and <br /> invertebrate production in wide areas of the river. Significant motion is <br /> reached in only 5% of the river so maintenance of side chaMels, etc <br /> will be limited. Floodplain inundation will be small and brief, but will <br /> provide some warm quiet-water habitats for growth and gonad <br /> maturation of endangered fish. The backwater at Walker SW A will <br /> provide some of this quiet habitat. <br />A verage, Dry; , 27,000 Initial motion is reached in 91 % of the river so in-channel scouring of <br />50-70% gravel and cobble bars will be wide spread. Wide spread areas with <br />exceedence clean substrates for egg deposition and incubation should provide for <br /> maximum reproductive success of Colorado pikeminnow and increased <br /> primary and secondary production. Significant motion is reached in <br /> 7% of the Colorado River, so maintenance of major habitat features <br /> 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 ofrazorback sucker and Colorado pikerninnow. <br />Average, Wet; , 35.000 Initial motion is reached in 98% of the river and significant motion is <br />30-50% reached in about 25%. In-channel habitats used by endangered fish <br />exceedence will be maintained in important river reaches; chaMel narrowing will <br /> be slowed or prevented. Flooding in and around Walker SW A will <br /> provide important floodplain habitats, but the extent of available habitat <br /> is not known. Widespread areas with clean substrate should provide for <br /> maximum reproductive success of Colorado pikeminnow and <br /> humpback chub, and increased primary and secondary production. <br />Moderately Wet; , 43.000 Initial motion is reached in 100% of the river and significant motion is <br />10-30% reached in about 42% of the river, creating and maintaining important <br />exceedence habitats for Colorado pikemiMow and razorback sucker in wide areas <br /> of the river. Floodplain habitats will be extensive, but the surface area <br /> of those habitats is not quantified Flows should exceed 35,000 cfs for <br /> at least 2 weeks to maximize the availability of floodplains habitats to <br /> young-of-year razorback sucker. <br /> <br />l <br /> <br />I <br /> <br />I <br /> <br />J <br /> <br />r <br /> <br />Draft Final Report <br />January 27, 2000 <br /> <br />4-20 <br /> <br />Chapter 4 <br /> <br />I <br /> <br />I <br />