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<br />correlated; (3) outliers and historical data were considered during the <br />development of flood flow frequency relationships for each gaging station; <br />and (4) developing regional relationships relating basin area to peak <br />discharge for the 10-, 50-, 100-, and 500-year floods. <br /> <br />The regional relationships relating basin area to peak discharge for the 10-, <br />50-, 100-, and 500-year floods thus established were employed to compute <br />the peak discharges used for detailed hydraulic analyses at various locations <br />for each of the 10-, 50-, 100-, and 500-year floods, and 100-year peak <br />discharges for the approximate methods. The regional relationships were <br />considered to be valid only for watersheds having drainage area larger than <br />10 square miles which is the lower limit of the gaging stations used in <br />regression analyses. Therefore, for Cornet Creek, which has a drainage area <br />of 2.38 square miles, SCS Curve Number technique was used to compute the <br />100-year flood discharge (Reference 9). The 10-, 50-, and 500-year flood <br />flows on Cornet Creek were also estimated from the frequency-discharge <br />curve drawn parallel to the curve obtained from the regression values. <br /> <br />:' <br /> <br />.. <br /> <br />y <br /> <br />Peak discharges for the 10-, 50-, 100-, and 500-year floods of each stream <br />studied in detail in the community are shown in Table 2. <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of the streams in the community <br />are carried out to provide estimates of the elevations of the floods of the <br />:;;elected recurrence intervals along each stream studied in detail. <br /> <br />Cross section data for streams in the area were obtained from aerial <br />photographs (Reference 10); the below-water sections were obtained by field <br />measurement. All bridges and culverts were measured to obtain elevation <br />data and structural geometry. <br /> <br />Locations of selected cross sections used in the hydraulic analyses are shown <br />on the Flood Profiles (Exhibit 1). For stream segments for which a flood way <br />is computed (Section 4.2), selected cross section locations are shown on the <br />Floodway Map (Exhibit 2). <br /> <br />Roughness coefficients (Manning's "n") were estimated by field inspection at <br />each cross section and checked for reasonableness against a recognized <br />standard text (Reference 11). Roughness values for the main channel range <br />from 0.035 to 0.050; roughness values for the flood plain range from 0.05 to <br />0.10. <br /> <br />": <br /> <br />On Cornet Creek, as evidenc~d in 1914 and 1969, the flood flows carried a <br />great deal of debris and mud, and shallow flooding prevailed in Telluride <br />whenever major floods occurred. In this regard, mudflow was considered in <br />the hydraulic analysis. A 20 percent water content in the mudflow was <br />assumed, which in turn yielded a 100-year mudflow discharge of 1,500 cubic <br /> <br />.;: <br /> <br />8 <br />