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<br />3.1 Hydrologic Analyses <br /> <br />Hydrologic analyses were carried out to establish peak discharge- <br />frequency relationships for each flooding source studied by <br />detailed methods affecting the community. <br /> <br />Peak floodElnws on the White River were computed from a statisticnl <br />analysis ot 73 years of gaged data. A log-Pearson Type III <br />frequency distribution was used in the analysis and three sets of <br />discharges were computed from a station skew, a regional skew, and <br />a weighted skew coefficient. For further comparisons, a set of <br />discharges was computed from a Gumbel extreme value distribution <br />and Hazen plotting positions for the 66-year period of record from <br />1910 to 1976. Separat ion of the gaged data into snowmel t and <br />rainfall categories was not considered. <br /> <br />Several forms of regional comparisons were made as an aid 1n <br />evaluating and interpreting the statistical flood frequency <br />analysis. These include flood discharges calculated from regional <br />multiple regression equations (TM-I, Reference 2), the index flood <br />method (WSP 1683, Reference 3), and comparisons with runoff (CSM) <br />ratios for adopted 100-year frequency flood discharges in northwest <br />Colorado. <br /> <br />The two frequency curves were assumed to represent independent <br />events and a composite flow-frequency curve was developed tor each <br />gaging station. A regional regression analysis was then made to <br />determine peak flow as a function of drainage area and return <br />period (Reference 4). Flow data on the White River were based on <br />the following USGS stream gages: <br /> <br />Gal1;e <br /> <br />Gage Number <br /> <br />Years of Record <br /> <br />White River near Watson, Utah <br />White River near Rangely, <br />Colorado <br />White River near Meeker, <br />Colorado <br /> <br />09306500 <br /> <br />51 <br /> <br />09306300 <br /> <br />8 <br /> <br />09304800 <br /> <br />70 <br /> <br />Peak discharge-drainage area relationships for the White River are <br />shown in Summary of Discharges (Table 1). <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of flooding from the <br />sources studied were carried out to provide estimates of the <br />elevations of floods of the selected recurrence intervals. <br /> <br />Locations of selected cross sections used in the hydraulic analyses <br />are shown on the Flood Profiles (Exhibit 1). <br /> <br />The water-surface elevations for <br />methods were computed through <br />Engineers HEC-2 step-backwate,- <br /> <br />the streams studied by detailed <br />use of the U.S. Army Corps of <br />computer program (Reference 5). <br /> <br />5 <br />