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result in a flow increase of 16,200 cfs and a stage change of 4, 7 feet, while an increase of 23,000 cfs to 33,200 cfs will result in a flow increase of 10,200 cfs and a stage change of2,9 feet at the confluence of the LCR At an upramp rate of4,000 cfs per hour, this stage change of2,9-4,7 feet is expected to occur in a period of about 2,6-4,0 hours, The downramp rate of 1,500 cfs per hour will take about 6,8-10,8 hours for flows to return to present operating range, ~ I ~ ~ This stage change of up to 4,7 feet over a period of4,O hours will produce dramatic and rapid changes in shoreline habitats used primarily by juvenile humpback chub, This habitat destabi1ization will be exacerbated by the downramp or return to present operations, The shoreline habitat changes include inundation and virtual elimination of all backwaters used as nurseries and rearing areas by young native fishes (Arizona Game and Fish Department 1996a, 1996b), and changes in the composition of the shallow, sheltered shoreline zone (<1 m, <0,3 m1s) used by juvenile humpback chub, Increases in stage of this magnitude often result in this shallow shoreline zone moving upslope, Depending on shoreline type, suitable habitat may remain available with increasing stage, or habitat quality may change and force fish to find alternative habitats, For example, a continuous talus slope may continue to provide suitable habitat, but talus sloping from steep cliffs is likely to be unsuitable for cover and low velocity habitat, Conversely, a shoreline with sand beach-unsuitable habitat because of lack of cover-may become talus with increasing stage and hence suitable habitat,juxtapositioning of shoreline habitats leads to destabi1ization that can force the young fish to seek alternative locations at additional energy expenditure and increased exposure to predation by brown trout and rainbow trout, ';; ~ ~ ~.. it,,: :,' The shallow shoreline habitats are used primarily by juvenile humpback chub (ages 0-2) up to about 175 mm TL, The most abundant age of chubs along the shorelines are the young This g- of-the-year (YOY; Le" age 0), which are usually 40-80 mm TL at 7 months of age (i,e., October), Swimming abilities of humpback chub up to 134 mm TL have been shown to be signifiClllltly reduced by cold water temperatures; releases from Glen Canyon Dam range from 8. C to 10. C, and warm to 10.C to 12.C at the confluence of the LCR. Although the high release of31,000 cfs is not expected to signifiClllltly affect river temperature, the likelihood that the juvenile chubs would be forced to leave the protective cover of their shoreline habitats would result in downstream displacement of fish and increased exposure to predation by brown trout and rainbow, A large population of brown trout exits in Bright Angel Creek and in the Colorado River near the confluence of that tributary. These fish spawn in late faD, and are very active feeders during September-November, Large numbers of brown trout are usually seen near the confluence of the Lca in fiIll. The cold water temperatures, in the range of those in the Colorado River below Glen Canyon Dam, have been demonstrated to effect the swimming ability of humpback chub up to 100 mm TL, When cold temperatures are combined with displacement, vulnerability to predation may be increased even further, Mid-channel habitats used by adults, such as large eddy complexes. are not expected to change dramatically enough to adversely modifY habitat of adult humpback chub, The release is not expected to affect spawning habitat of humpback chub, ~( ~: :~:... ~i i:~ ~ ~;~ :~~ ~;~ ;:) ~: i~ ",., #i: ~;;; ,", :* ~ ~ I .\1;; ;,~~i .;.;' . . ,.;-' 20