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<br />antecedent soil moisture condition (AMC-II). <br />versus-drainage-area data from this analysis were <br />regression line computed for several frequencies. <br /> <br />The dlscharge- <br />plotted, and a <br /> <br />A regional curve was developed for snowmelt flood events using <br />streamgage data from 8 streamgages ih the area. Thelog-Pearsdn <br />Type III frequency distribution (as defined in WRC Bulletin l7-B) <br />was used with a regional skew weighted with each computed station <br />skew. The data were plotted and frequency lines were drawn. <br /> <br />The two regional discharge frequency-drainage <br />(rainfall and snowmelt) were combined using <br />probability equation: <br /> <br />area curves <br />a standard <br /> <br />P(comb)=P(snow)+P(rain)-(P(snow)xP(rain)). <br /> <br />This combined regional curve is proposed for studies along the <br />Colorado River tributaries from the De Beque vicinity to Glenwood <br />Springs, Colorado. <br /> <br />Peak discharge-drainage area relationships for Roan Creek are <br />shown in Table 1. <br /> <br />TABLE 1. SUMMARY OF DISCHARGES <br /> <br />Flooding Source <br />and Location <br /> <br />Drainage Area <br />(SQ. miles) <br /> <br />Peak Discharge (cfs) <br />10-Year SO-Year 100-Year SOO-Year <br /> <br />Roan Creek <br />At the confluence with <br />the Colorado River <br /> <br />507.5 <br /> <br />3,650 <br /> <br />7,400 <br /> <br />9,700 <br /> <br />17,500 <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteri st ics of flooding from the <br />source studied were carried out to provide estimates of the <br />elevations of floods of the selected recurrence intervals. <br /> <br />Cross section data and reach length information were obtained <br />from photogrammetric maps prepared especially for this study with <br />contour intervals of 2.0 feet and a scale of 1:4,800 (Reference <br />6) . <br /> <br />Locations of <br />analyses are <br />also shown on <br /> <br />selected <br />shown on <br />the Flood <br /> <br />cross sections used in the <br />the Flood Profiles (Exhibit 1), <br />Insurance Rate Map (Exhibit 2). <br /> <br />hydraulic <br />and are <br /> <br />The U.S. Army Corps of Engineers HEC-2 computer program was used <br />to perform water-surface profile computations (Reference 7). <br />Several bridges and culverts exist along the channels through the <br />study reach. Dimensions for these road crossings were determined <br /> <br />6 <br />