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the bedrock and created a deep thalweg which scours during high flows and fills with sediment e during low flow. Ingrown bends tend to hold the position of the river at a location and limit the opportunity for the river to migrate across the floodplain or canyon bottom. Most natural river cross sections have a more complex behavior than conventional hydraulic geometry predicts. Channel dimensions are generally dependent on the discharge, which is a function of the watershed and the energy dissipated by the stream in transporting sediment. The bed and bank sediment govern the channel shape. Generally, channels with silty banks tend to have narrow and deep cross sections whereas rivers with sandy erodible banks are usually wide and shallow (Richards, 1982). Changes in the channel-forming discharge, sediment load and bed material sizes are affecting the Green River channel geometry. Vegetation encroachment also appears to be playing an increasing role in defining the channel cross section. A shift from a bedload-dominated stream to suspended load stream is another important process that may be affecting the channel morphology. Although the study reaches have virtually identical slopes, the Ouray reach has an average bankfull width that is approximately 110 ft wider (680 ft vs. 570 ft) even though the mean annual discharge in Canyonlands is significantly greater. The Green River has several tributaries (White, Duchesne, Price and San Rafael Rivers) with large sediment loads between the Ouray and Canyonlands reaches. Alluvial channels have the ability to adjust their morphology to the downstream changes in discharge and sediment load. Generally, a downstream increase in channel width is concomitant with a downstream increase in discharge. e If the downstream average channel width is narrower, then it follows that the corresponding downstream average depth and velocity must be greater. Hydraulic geometry relationships for alluvial channels indicate that channel width w is proportional to discharge Q as defined by: W DC Qb where the exponent b varies from 0.42 to 0.53 (Julien and Simons, 1984). Based on the mean annual peak discharge, the Canyonlands average channel width should have been approximately 1.2 times wider than the Ouray reach. However, the reverse is true; the Ouray topwidths average 1.2 times the Canyonlands topwidths at bankfull discharge. Bed Material and Bed Forms Bed material samples were collected in each study reach during the three data collection trips. These data are presented in Appendix B of this report. The sediment sampling program was not meant to be a comprehensive investigation of bed material variation, but rather an attempt to evaluate the following conditions: · Relative difference in bed material size between the two study reaches approximately 200 miles apart. e 17