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<br />001120 <br /> <br />t-'ABE 15 <br /> <br />Thll year-round base flow of300 cubic feet per second (cfs) insures survival offish ond other <br />aquatic life, precludes vegetation establishment in the active channel, and pro\'ides II!d eDbances <br />. the aesthetic charac1er of the river and canyon. A flow of 300 cfs provides favorabJ'1I habtiat <br />conditions for virtually ever life stage of rainbow and brown trout, Flows below 300 cis <br />significantly reduces spaWDing habitat necessary for the reproduction of both rainb~jlt' and brown <br />trout, and total wetted surface area. <br /> <br />" <br />Spring peak flows were a sisnificant component of the hydrograph (flow conditions) that <br />produced and maintained the scenic and aesthetic conditions existing at the time BIalIk Canyon <br />National Monument was established in 1933. Peak flows contra) riparian vegetation! entrain and <br />transport sediment through the cany~ serve as spawning cues for fISh, remove sediment from <br />spawning beds~ maintain ChBnllel forming processes, and enhance visitor experiences by <br />contributing to the sights and sound oftbe Gunnison River. Figure 1 depicts the relationship <br />betWeen April through July unregulated inflow to Blue Mesa Reservoir and the histolfic one-day <br />peak flow for the Gunnison River below the Gunnison Tuunel for the years 1937~ 1965. This <br />relationship serves as the basis for future peak flow recommendations. The peak flow in anyone <br />year will depend on snowpack conditions or forecasted nm.off and will vary from ye,lIl'-to-year as <br />snoWpack conditions vary. For any given vOllue offorecasted inflow, the equation of'lhe iine <br />shown in Figure 1 will be used to determine the maximum one-day peak for that year. Analysis <br />of pre-dam peaks and associated ramping rates has shown that the Bureau ofReclammion's <br />current ramping rates are equivalent to those of the natural pre-dam hydrograph. Theue ramping <br />rates are reflected in the claim. <br /> <br />At the time the Monument was created, streamside vegetation within t~e canyon was I;ontrolled <br />by both peak flows (i.e., scour) and prolong~d inundation, with peak flows beini the dominant <br />mechanism of vegetation removal. The cJaim~s shoulder flows capture the period of))rolonged <br />innundation that funher controls riparian vegetation. They also transpon sedixnent, mllintain <br />aquatic biota, and eMance visitor experience/appreciation of the river, Figure 1 also nlates the <br />8S..day shoulder flow to the same April through July unregulated inflow to Blue MeS81, Once the <br />mal~tude oitha peak flow is determined, Figure 1 and the associated equations are ulied to <br />determine the magnitude of the 8S-day shoulder flow necessary to maintain historic cunyon <br />clearing and bottom width. <br /> <br />Thus, in any one year, the recommended hydrograph will be comprised of a ye~.rounll base flow <br />of 300 cfs, and given tlte forecasted run..off (expressed as April through July unregwaltcd inflow) <br />a peak flow and 8S-day or shoulder flow as determined from Figure 1. Figures 2,3, aJlld 4 depict <br />the application of the National Park Service flow recommendations to a "nonnal~l' "dl:"" and <br />"wetll water year, respectively. <br /> <br />tft <br />