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<br />Frequency analyses for Los Pinos River below Vallecito Dam at Bayfield <br />were based on the operational records of Vallecito Reservoir (Refer- <br />ence 1); streamflow records at the Ignacio gage, a U.S. Geological <br />Survey gage with 22 years of record; and the regional relationships <br />developed for the Upper San Juan River basin (Reference 2). The <br />operational records of Vallecito Reservoir and streamflow records at <br />the Ignacio gage were used to establish the peak discharge-frequency <br />relationships at the outlet of the reservoir and the gage, respective- <br />ly. Peak discharges of selected recurrence intervals at Bayfield <br />were determined by adding discharges of selected recurrence intervals <br />produced by the drainage area downstream of the Vallecito Reservoir <br />to the corresponding peak discharges at the reservoir outlet. <br /> <br />Discharges of selected recurrence intervals contributed from drainage <br />areas downstream of Vallecito Reservoir were determined applying the <br />regional relationships established for the Upper San Juan River <br />basin. <br /> <br />Peak discharge-drainage area relationships for Los Pinos River are <br />shown in Table 1. <br /> <br />Table 1. <br /> <br />Summary of Discharges <br /> <br />Drainage Area <br />(Square Miles) <br /> <br />Peak Discharges <br />(Cubic Feet per Second) <br />10-Year 50-Year 100-Year 500-Year <br /> <br />Flooding Source <br />and Location <br /> <br />Los Pinos River <br />U.s. Highway 160 <br />Alternate <br /> <br />349 <br /> <br />3000 <br /> <br />5000 <br /> <br />6000 <br /> <br />9300 <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of streams in the community <br />were carried out to provide estimates of the elevations of floods of <br />the selected recurrence intervals along the stream studied in the <br />community. <br /> <br />Cross section data for streams in the area were obtained from aerial <br />photographs (Reference 3); the below-water cross sections were obtain- <br />ed by field measurement. All bridges and culverts were measured to <br />obtain elevation data and structural geometry. <br /> <br />Locations of selected cross sections used in the hydraulic analyses <br />are shown on the Flood Profiles (Exhibit 1). For stream segments <br />for which a floodway is computed (Section 4.2), selected cross <br />section locations are also shown on the Floodway Map (Exhibit 2). <br /> <br />5 <br />