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<br />001020 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />for the overbank areas to analyze flow stability. For capacity purposes, the <br />valves of 0.040 and 0.065 were used. <br /> <br />Further analysis of the history of Cherry Creek and the floodplain <br />revealed three important factors. First, a review of the aerial photographs <br />showed that the 1 argest fl ood (i.e., June, 1 965) had on 1y mi nor effect on the <br />horizontal alignment of the channel. Most of the horizontal movement probably <br />occurred at intermediate flows. Flow instability is more of a concern in the <br />main channel area than in the overbank area. This factor was confirmed by the <br />field measurements of past floods. The highest bankfull measurement was 4000 <br />cfs with an average velocity of 12 fps, The Froude Number was estimated to be <br />in the transitional range (i.e., 0.8 < Fr < 1.2). To maintain a fixed align- <br />ment at bankfull discharges, the main channel would be excavated to more <br />closely match the average active bed width (i.e., 230 feet) and the banks would <br />be protected by revetment where required. <br /> <br />The second factor was that the bed elevation changed considerably in local <br />areas during major floods (i .e., degraded approximately 2.7 feet at Arapahoe <br />Road during the 1965 flood). This would increase the depth of flow during the <br />flood and therefore decrease the i nstabil i ty of the flow since the Froude <br />Number is inversely proportional to the depth. The bed level subsequently <br />rose due to the deposition of materials carried by lesser flows. <br /> <br />-28- <br />