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<br />3.1 Hydrologic Analyses <br /> <br />Hydrologic analyses were carried out to establish the peak discharge- <br />frequency relationships for floods of the selected recurrence inter- <br />vals for each stream studied in detail in the community. <br /> <br />The hydrologic analysis for this study is covered in the Flood <br />Insurance Study for Eagle County, Colorado (Reference 5). The <br />analysis was completed for both snowmelt and rainfall events. <br /> <br />Separation of the snowmelt and rainfall events was completed using <br />u.s. Geological Survey data. The data showed that, except for small <br />basins less than approximately 10 square miles, the snowmelt events <br />yielded higher discharge peaks than the rainfall events for the flow <br />frequencies used in this report. Using u.s. Geologica1 Survey snowmelt <br />event gage records from several gages along the Eagle River, regres- <br />sion equations were developed to predict 10-, 50-, 100-, and 500- <br />year frequency discharges as a function of drainage area. The <br />equations were of the form: <br /> <br />Discharge <br /> <br />(. }0.7 <br />constant x dralnage area <br /> <br />The discharge-drainage area curves were "then modified to include the <br />. effect of rainfall events on smaller drainage areas using a synthetic <br />hydrograph approach. <br /> <br />Flood dicharges for the 10-, 50-, 100-, and SOG-year floods on the <br />Eagle River and Turkey Creek were calculated using the regression <br />equations directly (Reference 5). <br /> <br />Peak discharge-drainage area relationships for Eagle River and Turkey <br />Creek are shown in Table 1. <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of streams in the commu- <br />nity were carried out to provide estimates of the elevations of <br />floods of the selected recurrence intervals along each stream <br />studied in the community. <br /> <br />Water-surface elevations of floods of the selected recurrence inter- <br />vals were computed through use of the u.s. Army Corps of Engineers <br />HEC-2 step-backwater computer program (Reference 6). <br /> <br />Cross sections for the backwater analyses for water-surface profiles <br />of the Eagle River and Turkey Creek were field surveyed. All bridges <br />were field checked to obtain elevation data and structural geometry. <br /> <br />5 <br />