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<br /> <br />474 <br /> <br />Topographic Response of a Oar <br /> <br />" <br /> <br />t <br /> <br /> <br />Q-SO <br />Maximum value - 249.7 dylem' <br /> <br />~ - <br />ff <br /> <br />f/j llfl <br /> <br /> <br />Q - 275 <br />Maximwn IIiI1ue - 92.5 dy/ em' <br /> <br /> <br /> <br />Q - 475 <br />Maximwn value -138 dy/ em' <br /> <br />Fig. 4. Distribution of boundary shear stress in tbe Ouray reacb at discharges of 50 m3/s, <br />215 m3/s, and 415 m3/s. <br /> <br />The computation of topographic evolution process described above repeated <br />iteratively until either the desired time interval has passed or a quasi-steady state is <br />reached. (Quasi-steady state refers to the situation in which the bar form is <br />well-developed and has a constant shape, although it still may migrate <br />downstream.) For this investigation, the evolution models were used primarily to <br />determine the response of bed topography to various discharges, rather than to <br />calculate the steady-state topography. <br /> <br />Response of Flow ~ Ch~el Topograp~y <br /> <br />" Lateral and downstream variations in" boundary shear stress and veI'tically- " <br />averaged velocity are due to changes in channel area, channel curvature, and bed <br />topography. Channel area varies greatly through the Ouray reach, and has a <br />significant influence on the characteristics of flow and sediment transport. Bankfull <br />channel area varies {rom 580 m2 near cross section 7 to 400 m2 near cross section <br />36. Channel area decreases by 25 percent between cross section 7 and cross section <br />20, located at the bar crest. The distributions of boundary shear stress in the Ouray <br />reach computed for 3 discharges, 50 m3/s, 275 m3/s, and 475 m3/s, are compared in <br />Figure 4. Similarly, the distributions of verticaliy-averaged vefocity computed for <br />