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<br />2.4 Flood Protection Measures <br /> <br />At the present time, there are no flood-protection measures within <br />the study area other than small levees constructed by local <br />entities. However, flow of the Yampa River is slightly affected by <br />Catamount Lake, Lester Creek Reservoi r (a1 so known as Pearl Lake) <br />and Steamboat Lake. These lakes do not provide flood protection. <br /> <br />3.0 ENGINEERING METHODS <br /> <br />For the flooding sources studied by detailed methods in the community, <br />standard hydrologic and hydraulic study methods were used to determine <br />the flood hazard data required for this study. Flood events of a <br />magnitude which are expected to be equaled or exceeded once on the <br />average during any 10-, 50-, 100-, or 500-year period (recurrence <br />interval) have been selected as having special significance for <br />floodplain management and for flood insurance rates. These events, <br />commonly termed the 10-, 50-, 100-, and 500-year floods, have a 10, 2, <br />1 and 0.2 percent chance, respectively, of being equaled or exceeded <br />during any year. Although the recurrence interval represents the 10ng~ <br />term average period between floods of a specific magnitude, rare floods <br />could occur at short intervals or even within the same year. The risk <br />of experiencing a rare flood increases when periods greater than 1 year <br />are considered. For example, the risk of having a flood which equals <br />or exceeds the 100-year flood (1 percent chance of annual exceedence) <br />in any 50-year period is approximately 40 percent (4 in 10), and for <br />any 90-year period, the risk increases to approximately 60 percent (6 <br />in 10). The analyses reported herein reflect flooding potentials based <br />on conditions existing in the community at the time of completion of <br />this study. Maps and flood elevations will be amended periodically to <br />reflect future changes. <br /> <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 discharge-drainage area re1atiortships for the Yampa and Elk <br />Rivers are shown in Table 1. <br /> <br />TABLE 1. SUMMARY OF DISCHARGES <br /> <br />Flooding Source <br />and Location <br /> <br />Drainage Area <br />(Square Miles) <br /> <br />Peak Discharges (cfs) <br />10-Year SO-Year 100-Year 500-Year <br /> <br />Yampa River <br />At downstream end of <br />the study reach <br /> <br />666 <br /> <br />__1 <br /> <br />1 <br /> <br />8,930 <br /> <br />__1 <br /> <br />Approximately 250 feet <br />upstream of the Steamboat <br />Springs corporate limits <br /> <br />520 <br /> <br />__1 <br /> <br />1 <br /> <br />5,000 <br /> <br />1 <br /> <br />5 <br />