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~Ya.~ 1'::/~ J ~:11i d <br />tO~vov~.rww <br />the reach had to be made. Since a rigorous time of travel study <br />• was not possible during this investigation, the hydrologists <br />used professional judgement in making an estimate. <br />The time of travel over [he reach of interest includes <br />the effects of both rapid and slow moving sections of the river. <br />Therefore, an estimate of the time of travel was made using a <br />weighted average of observed velocities. This calculation was <br />based on the data given below in Tab 1e 4-2: <br />TABLE 4-2 <br />Estimated % of <br />Average of Total Reach Having River tiles Having `files/Avg. Velocity <br />Velocity (fps) Stated Velocity Stated Velocit}• (mi) (mi/fps) <br />' 2 10% 0.46 0.23 <br />. 1 50% 2.3 2.1 <br />0.5 <br />~ 30% <br />0 1.38 2.76 <br />4 <br />6 <br />0.1 1 <br />% 0.45 . <br /> 4.6 9.69 <br /> <br />4.6 miles/9.69 mi/fps = 0.5 fps <br />iJ <br />i The Colorado District of the U.S. Geological Survey <br />performed a time of travel study on a 90-mile reach of the Yampa <br />~ River in September, 1978. This included the reach of interest <br />in this study. The mean velocity of the Yampa, for about 17 <br />miles below Craig, was determined to be about 0.66 fps at a flow <br />of 150 cfs (USGS, 1978). This can be extrapolated to the flow <br />range encountered in this study. <br />i The Manning equation for uniform open channel flow is: <br />~ = 1.49 R 2/3 S 1/2 <br />n <br />• <br />4-7 <br />