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0025J7 The year-round base flow of3oo cubic feet per second (efs) insures survival offish llnd other aquatic life, precludes vegetation establishment in the active c:hannel~ and provides aad enhances . the aesuletic character of the river and canyon. A flow of 300 efs provides favorabl,ll habtiat conditio:os for virtually ever life stage of rainbow and brown trout. Flows below 300 cis significantly reduces spawning habitat necessary for the reproduction of both rainbow and brown trout, and total wetted surface area. " Spring peak flows were a significant component of the hydro graph (flow conditions) that produced and maintained the scenic and aesthetic conditions existing at the time Blallk Canyon National Monument was established in 1933. Peak flows control riparian vegetation~ entrain and transport sediment through the canyon, serve as spawning cues for fish. remove sediment from spawninJI beds, maintain channel forming processes, and enhance visitor experien ceSI by contributing to the sights and sound of the Gunnison River. Figure 1 depicts the rebrrionship betWeen April through July unregulated inflow to Blue Mesa Reservoir and the histolric one-day peak flow for the Gunnison River below the Gunnison Tunnel for the years 1937-l9Ei5. This relationship serves as the basis for futUre peak flow recommendations. The peak flow in anyone year will depend on snowpack conditions or forecasted run-off and will vary from ye,I\l'-to.-year as snowpack conditions vary. For any given V;tlue offorecasted inflow, the equation of ' the line shown in Figure 1 will be used to detennine the maximum one-day peale for that year, Analysis ofpre-da:m peaks and associated ramping fates has shov.rn that the Bureau ofReclam~\lion's current ramping rates are equivalent to those oithe natural pre-dam hydro graph. TheIle ramping rates are reflected in the claim. At the time the Monument was created, streamside vegetation within the canyon was l;ontrolled by both peak flows (i.e., scour) and prolonged inundation, with peak flows bein2 the d,ominant mechanis:m of vegetation removal. The cJaim's shoulder flows capture the period of prolonged innundati,on that funher controls riparian vegetation. They also transport sediment, mllintain aquatic biota, and enhance visitor experience/appreciation of the river. Figure 1 also I'elates the 85-day sh.oulder flow to the same April through July u."U'egulated inflow to Blue Mesa\, Once the nUiln,itudtC oCthe peak flow is determined, Figure I and the associated equations are u!:ed to detennine the magnitude ofthe 8S-day shoulder flow necessary to maintain historic cllnyon clearing and bottom width. Thus, in any one year, the recommended hydro graph will be comprised of a YElar.round base flow of300 cfs, and given the forecasted run-off (expressed as April through July unregula1tcd inflow) . a peak flow and 8S-day or shoulder flow as determined from Figure 1. Figures 2,3, 31lld 4 depict the application oithe National Parle Service flow recommendations to a "nonnal," "dry" and I'wet" water year, respectiveJy. .r