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<br />Channel roughness factors (Manning's "n") used in the hydraulic <br />computations were chosen by engineering judgment and based on field <br />observations of the streams and flood plain areas. The ranges of <br />"nll values for the streams in this study are as follows: <br /> <br />St:ream Name <br /> <br />Manning's <br />Channel <br /> <br />"ntl Values <br />OVerbank <br /> <br />Blue River <br />l'Iillow Creek <br />Straight Creek <br />Tenmile Creek <br />West Tenmile Creek <br />Snake River <br />Soda Creek <br />Meadow Creek <br /> <br />0.040 <br />0.040 <br />0.035-0.04C <br />0,040 <br />0.035-0.050 <br />0.040 <br />0.035 <br />0.035-0.040 <br /> <br />0.080-0.100 <br />0.100 <br />0.050-0.100 <br />0,060-0.100 <br />0.030-0.070 <br />0.060-0.100 <br />0.060 <br />0.050-0,100 <br /> <br />Starting water-surface elevations for Blue River were calculated <br />using the slope-area method at the downstream end of BluE.River. <br />For Willow Creek and Straight Creek, starting water-surface eleva- <br />tions were chosen from the water-surface profiles for Blue River. <br />For Tenmile Creek, Snake River, Soda Creek, and Meadow Creek, <br />starting water-surface elevations were taken at Dillon Reservoir. <br />Starting water-surface elevations for West Tenmile Creek were <br />chosen from the water-surface profiles for Tenmile Creek. <br /> <br />Flood profiles were drawn showing computed water-surface elevations <br />to an accuracy of 0.5 foot for floods of the selected recurrence <br />intervals (Exhibit 1). The 10-, 50-, and 500-year profiles for Blue <br />River were not presented due to the limited scope of the study. <br /> <br />Due to the meandering nature of Meadow Creek, a Profile Base Line is <br />presented to show tne actual flow pattern during a IOO-year flood. <br /> <br />Snake River, near its upstream limit of study, splits into two channels <br />under normal flow conditions. However, during the IOO-year flood, one <br />flow is actually present. A Profile Base Line is presented for this <br />area to show the 100-year flood flow path. <br /> <br />Shallow flooding along Blue River, West Tenmile Creek, and Snake <br />River was determined by hand calculations based on normal depths. <br /> <br />Approximate IOO-year flood elevations for Blue River, Snake River, <br />Soda Creekl and French Gulch were determi~ed using normal-depth <br />calculations in conjunction with topographic maps (Refere~ces 12 <br />and 19 through 26). <br /> <br />Approximate IOO-year flood elevations for South Barton Gulch were <br />determined by normal-depth hand calculations. <br /> <br />13 <br />