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sand has the potential to move either in suspension or in contact with the bed, with the threshold occurring at flows between 125 and 150 m3/s (4500-5500 ft3/s). Intensive field measurements, coupled with results from one-dimensional hydraulic model, were used to assess variations in flow properties with discharge in a 0.8-km study reach. The field measurements indicate that there is a relatively abrupt transition in the water-surface width and wetted area of the channel between discharges of 125 and 175 m3/s (4500-6200 Wls). At discharges < 125 m3/s most of the flow is confined to the baseflow channel, and more than half the channel perimeter is dry. At discharges > 125 m3/s flow begins to cover low-lying bar surfaces; width increasing steadily from there until -280 m3/s when most of the channel bed is inundated. This discharge is consistent with flow-modeling results indicating that the threshold for initial motion of the bed material in this reach is exceeded at a discharge of 286 m3/s. That value is within 3% of the value recommended in previous reports. Adjusting the model results to account for spatial variations in grain size increases the threshold slightly, indicating there is very little bed load transport within the reach at flows less than 300 MN (10,600 ftl/s). The results discussed in this report are broadly consistent with the results presented in previous reports, therefore, all of the previous recommendations are retained. It is assumed that periodic movement of the gravel bed material of the Colorado River is important for maintaining habitats used by native fishes and other aquatic organisms. It also assumed that periodic movement of the bed material is important for maintaining a channel with some morphologic complexity or heterogeneity. Finally, it is assumed that the mass balance of sediment carried by the Colorado River must be maintained over the long run, otherwise there will be continued narrowing and simplification of the channel, and a loss of associated, habitats. The following discharges, including frequency and duration, are recommended to achieve these purposes: iii