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morphology of the Colorado River has changed little in the last decade. Vertical and lateral <br />deposition of fine sediment occurred in all of the side channels monitored, however, the changes <br />detected in these features were again relatively minor. <br />Additional analyses of suspended sediment records from gauging stations in the study <br />area reconfirm the importance of late-spring flows for carrying sediment. The analysis indicates <br />that roughly 80% of the sediment carried in suspension consists of silt- and clay-sized particles. <br />Concentrations of suspended sediment at all gauging stations are consistently higher on the rising <br />limb of the hydrograph than they are on the falling limb, thus the total annual sediment load is <br />dominated by late-spring flows. Both sediment concentration and water discharge are high in the <br />spring, thus the total annual sediment load is dominated by flow conditions during this period of <br />time. About 20% of the total suspended sediment load consists of sand. This sediment reaches a <br />peak 2-3 weeks after the peak in water discharge, and not far in advance of the typical period of <br />time when Colorado pikeminnow are preparing to spawn. It is not clear that the sand moving at <br />this time of the year represents a problem in an ecological sense; however, it is evident that the <br />sand has the potential to move either in suspension or in contact with the bed, with the threshold <br />occurring at flows between 125 and 150 m/s (4500-5500 ft3/s). <br />Intensive field measurements, coupled with results from one-dimensional hydraulic <br />model, were used to assess variations in flow properties with discharge in a 0.8-km study reach. <br />The field measurements indicate that there is a relatively abrupt transition in the water-surface <br />width and wetted area of the channel between discharges of 125 and 175 m3/s (4500-6200 ft /s). <br />At discharges < 125 m3/s most of the flow is confined to the baseflow channel, and more than <br />half the channel perimeter is dry. At discharges > 125 m3/s flow begins to cover low-lying bar <br />surfaces; width increasing steadily from there until -280 m3/s when most of the channel bed is <br />58