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<br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br /> <br />An estimated 302 million cubic meters of sediment were temporarily stored in <br />long-term potential sources and sinks, 95% of which was located in the valley bottom and <br />80% of which was in the lower reach. Most of the sediment consisted of rock types less <br />resistant to erosion. Grain-size analyses indicated that that potential sediment sources are <br />very poorly sorted and coarse skewed. Sediment in the main channel is more sorted than <br />sediment from potential sources, and main channel sorting improves downstream. The <br />fine component (ds, d16, dso) of the main channel sediment is coarser than that of <br />sediment sources, indicating that the finest component of introduced sediment is carried <br />downstream beyond the study reach. The coarser component (d84, d9o) of the main <br />channel sediment is significantly coarser than potential sources in the lower reach, <br />indicating that coarse material is entering the lower reach through downstream transport <br />from the upper reach. <br /> <br />The modern channel is primarily single-thread, pool-riffle in the upper reach and <br />braided in the lower reach. Both the upper and lower reaches of the study area are similar <br />to other braided channels based on published slope-discharge relationships for braided <br />channels. Historical evidence suggests that the North Fork of the Gunnison has been <br />primarily braided, although some reaches of the lower river have at times had a sinuous, <br />single-thread morphology. <br /> <br />Comparisons of control variables suggest that geology determines the trends of <br />the other watershed and reach scale controls. Sediment analyses and statistical model <br />selections indicate that geology also has a large influence on watershed sediment <br />dynamics. Results from the historical planform stability analysis show that geology <br />controls the location of channel changes in the study area, whereas climate controls the <br />magnitude of changes along the active channel. <br /> <br />However, human activities also influence sediment and channel dynamics. Coal <br />mining may have increased the frequency of hillslope mass movements and contributed <br />to higher sediment input to the main channel in the upper reach. The greatest channel <br />changes have occurred in the lower reach, where the natural bed material in the main <br /> <br />3 <br />