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<br />developed for the unsteady flow model were used to describe the channel geometry. The initial <br />ice cover bridging location was set at the Ouray Bridge at a surface ice concentration of 50%. <br />The initial stationary ice cover thickness was set based on the observations of ice cover thickness <br />during the 1997 field measurements. The frazil ice rise velocity was set at 0.001 ft/sec, the initial <br />floe thickness was set at 0.1 foot, and the model time step was set at 2 hours. The channel and <br />' ice cover roughnesses used in the UNET simulation described above were used in the ice <br />simulation. The calculated ice cover extent during each winter is shown in Figure 32 along with <br />the calculated water temperatures and the measured daily average air temperature for Vernal, <br />Utah. <br />Modeled results were in general agreement with the historical ice observations. The <br />model predicted formation of a stationary ice cover in the Green River every winter and the ice <br />cover progresses upstream relatively quickly during cold periods. The ice cover progressed <br />1 upstream as far as River Mile 300 in almost every winter. However, there was a large variation <br />in the length of time each winter that the ice cover remained at this location. During cold winters <br />it was predicted that the ice cover would extend past River Mile 300 for several months. During <br />mild winters, the ice cover would extend past River Mile 300 for two weeks or less. <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br /> <br />1 <br /> <br /> <br />19 <br />