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<br />u.s. Highway 40 traverses the study area in a general north-south <br />direction. Hydraulic structures under the highway have sufficient <br />capacity so that floodflows are generally unaffected. However, <br />north of winter park, insufficient capacity of the culvert under <br />u.s. Highway 40 does restrict flow from Leland Creek, on the west <br />side of the highway, from entering the Fraser River. <br /> <br />The Denver and Rio Grande Western Railroad also transects the valley <br />in a north-south direction. It is located at the western edge of <br />the valley and crosses all the tributaries included in this study <br />except Jim Creek. Some minor ponding at these crossings is expected <br />although most of the culverts do not flow full. <br /> <br />3.0 ENGINEERING METHODS <br /> <br />For the flooding sources studied in detail in the community, standard <br />hydrologic and hydraulic study methods were used to determine the flood <br />hazard data required for this study. Flood events of a magnitude which <br />are expected to be equaled or exceeded once on the average during 'any <br />10-, 50-, 100-, or SOO-year period (recurrence interval) have been selec- <br />ted as having special ,significance for flood plain management and for <br />flood insurance rates. These events, commonly termed the 10-, 50-, 100-, <br />and SOO-year floods, have a 10, 2, 1, and 0.2 percent chance, respectively, <br />of being equaled or exceeded during any year. Although the recurrence <br />interval represents the long term average period between floods of a <br />specific magnitude, rare floods could occur at short intervals or even <br />within the same year. The risk of experiencing a rare flood increases <br />when periods greater than 1 year are considered. For example, the risk <br />of having a flood which equals or exceeds the 100-year flood (l percent <br />chance of annual exceedence) in any 50-year period is approximately 40 <br />percent (4 in 10), and, for any 90-year period, the risk increases to <br />approximately 60 percent (6 in 10). The analyses reported herein reflect <br />flooding potentials based on conditions existing in the community at the <br />time of completion of this study. Maps and flood elevations will be <br />amended periodically to reflect future changes. <br /> <br />3.1 Hydrologic Analyses <br /> <br />Hydrologic analyses were carried out to establisq the peak discharge- <br />frequency relationships for each flooding source studied in detail <br />affecting the community. <br /> <br />Discharge values prepared by Worrall Engineers and presented in <br />their 1983 report (Reference 1) were used in this Flood Insurance <br />Study. Several key assumptions made in that analysis were reviewed <br />during the hydrology analysis of this study. A detailed summary <br />of the hydrologic analysis is contained in a separate Hydrology <br />Report to FEMA (Reference 2). <br /> <br />11 <br />