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Figure 18. Seasonal trends in discharge and the percentage of sand in suspended sediment <br />samples, Colorado River near Cameo, CO, Gunnison River near Grand Junction, and (c) <br />Colorado River near Colorado-Utah state line. <br />The trends in sand percentage indicate that in typical years the Colorado River and the <br />Gunnison River continue to transport sand in suspension for several weeks after the peak in the <br />annual hydrograph. Although the trends are somewhat irregular, the timing of the peak in sand <br />concentration at the three gauges occurs at roughly the same time (mid-June). If sand was <br />moving through this river system as a wave or pulse, then there should be a lag in the timing of <br />the peak percentage of sand in the downstream direction. This does not appear to be the case, <br />suggesting again that much of the sand in transport is derived locally, i.e. from the channel bed, <br />rather than discrete sources upstream. The observed patterns are probably not unnatural and it <br />would be reasonable to assume that, if this has always been the case, then the native fishes have <br />evolved to cope with these conditions. The key question is whether the timing of the peak in <br />sand transport has any effect on spawning, or the fishes preferences for spawning in certain <br />areas, and thus is there a reason to be concerned about changes in the timing of the peak? <br />41