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<br />rPl"ll;. ~;j <br /> <br />0012J6 <br /> <br />The yeararoWld base flow of 300 cubic feet per second (efs) insures survival offish and other <br />aquatic life, precludes vegetation establishment in the active charmel? and provides and enhances <br />, the aesthetic character of the river and canyon. A flow of 300 cis provides favorabl'll habtiat <br />conditions for virtually ever life stage of rainbow and brown trout. Flows below 300 cis <br />significantly reduces spawning habitat necessary for the reproduction of both rainbow and brown <br />trout, and total wetted surface area. <br /> <br />" <br /> <br />Spring peak flows were a sisnific~t component of the hydrograph (flow conditions) that <br />produced and maintained the scenic and aesthetic conditions existing at the time BJaok Canyon <br />National Monument was established in 1933. Peak flows control ripBrim vegetation~ entrain and <br />transport sediment through the canyon, serve as spawning cues for fash, remove sediIllent from <br />spawnin'J beds, maintain channel forming processes, and enhance visitor experiences by <br />contributing to the sights and sound of the Gunnison River. Figure 1 depicts the rebrlionship <br />between April through July unregulated inflow to Blue Mesa Reservoir and the historic one-day <br />peak flow for the Gunnison River below the Gunnison TUDIlel 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 V8Iy from ye.llr-to-ycar as <br />snowpack conditions vary. For any given vitlue offorecasted inflow, the equation olothe iine <br />shown in Figure 1 will be used to detennine the maximum one-day peak for that year. Analysis <br />ofpre-dam peaks and associated ramping rates has shown that the Bmeau ofReclanultion's <br />current ramping rates are equivalent to those of the natural pre-dam hydro graph. Theile ramping <br />rates are reflected in the claim. <br /> <br />At the time the MonUlnent 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 d.ominant <br />mechanism of vegetation removal. The claim's shoulder flows capture the period ofl)rolonged <br />innundation that further controls riparian vegetation. They also transpon sediment, muintain <br />aquatic biota. and enhance visitor experience/appreciation of me river. Figure 1 also nlates the <br />8S..day shoulder flow to the same April through July unregulated inflow to Blue Mess\. Once the <br />msan,itude of the peak flow is dctennined, Figure 1 and the associated equations are uHed to <br />detennine the magnitude of the as-day shoulder flow necessary to maintain historic canyon <br />clearing and bottom width. <br /> <br />Thus, in any one year, the recommended hydrograph will be comprised of a year..roUIIlJ base flow <br />of300 els, and given the forecasted run-off (expressed as April through July unregwaltcd inflow) <br />a peak flow and IS-day or shoulder flow as determined from Figure 1. Figures 2, 3, &Iud 4 depict <br />the application afthe National Park Service flow recommendations to a "nonnal," "cIr)"I and <br />"wet" water year, respectively. <br /> <br />" <br />