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Natural streamflows of the Colorado River are regulated by a series of storage reservoirs <br />and water diversions upstream of the study area. Data reported by Liebermann et al. [ 19891 <br />indicate that there are 24 reservoirs with a capacity greater than 6.2 x 106 m3 (-5,000 acre-feet) <br />upstream of the Colorado-Utah state line. A number of these reservoirs were built to store and <br />supply water to communities located on the east side of the continental divide, and on average <br />about 14 % of the annual flow of the Colorado River is diverted out of the basin. Most of the <br />storage reservoirs in the upper Colorado River basin were constructed in the period between <br />1950 and 1966. Reservoir operations have affected both the timing and magnitude of peak <br />snowmelt flows in the study area. Since 1950 instantaneous peak discharges of the Colorado <br />River and its major tributary, the Gunnison River, have decreased by and average of 29-43% <br />[Van Steeter and Pitlick, 1998]. However, in most years, runoff from unregulated or moderately <br />regulated tributaries is still sufficient to produce a prominent spring peak in the annual <br />hydrograph. Much smaller peaks associated with late-summer thunderstorms are also common. <br />The Colorado River carries moderately high sediment loads, increasing downstream from <br />1.5 x 106 metric tons per year at the US Geological Survey (USGS) gauging station near Cameo, <br />CO, to 3.4 x 106 metric tons per year at the USGS gauging station near the Colorado-Utah state <br />line [Pitlick and Cress, 2000]. At least 95% of the total sediment load consists of fine sediment <br />(silt and sand) carried in suspension [Pitlick and Van Steeter, 1998]. Much of the fine sediment <br />is derived from surface erosion of friable sedimentary rocks underlying the Roan Mesa. The <br />contribution of fine sediment from this area remains high. Coarse sediment (cobble and gravel) <br />is derived from local as well as distant sources. Although gravel is a minor component of the <br />total sediment load of the Colorado River, this material forms the bed of the channel, and <br />therefore provides habitat for benthic invertebrates as well as native and non-native fishes. <br />9