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<br />City of Steamboat Springs <br /> <br />No flood-control structures have an effect in the study area. Flood damage prevention <br />measures consist of emergency operations during floods and local floodplain <br />development ordinances. <br /> <br />Routt County <br /> <br />At the present time, no flood protection structures exist within the study area other than <br />small levees constructed by local entities. However, the Yampa River flow is slightly <br />affected by Catamount Lake, Lester Creek Reservoir (also known as Pearl Lake), and <br />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, standard hydrologic <br />and hydraulic study methods were used to determine the flood hazard data required for this <br />study. Flood events of a magnitude that is expected to be equaled or exceeded once on <br />average during any 10-, 50-, 100-, or 5oo-year period (recurrence interval) have been selected <br />as having special significance for floodplain management and for flood insurance rates. These <br />events, commonly termed the 10-, 50-, 100-, and 500-year floods, have a 10-, 2-, 1-, and <br />O.2-percent chance, respectively, of being equaled or exceeded during any year. Although the <br />recurrence interval represents the long-term, average period between floods of a specific <br />magnitude, rare floods 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 are considered. For <br />example, the risk of having a flood that equals or exceeds the loo-year flood (I-percent <br />chance of annual exceedence) in any 50-year period is approximately 40 percent; for any <br />9O-year period, the risk increases to approximately 60 percent. The analyses reported herein <br />reflect flooding potentials based on conditions existing in the community at the time of <br />completion of this study. Maps and flood elevations will be amended periodically to reflect <br />future changes. <br /> <br />3.1 Hydrologic Analyses <br /> <br />Hydrologic analyses were performed to establish the peak discharge frequency <br />relationships for floods of the selected recurrence intervals for each stream studied in <br />detail. <br /> <br />Burgess Creek.. Elk River.. Walton Creek.. and Yampa River <br /> <br />Standard flood frequency analysis was used to develop peak: discharges for the <br />selected return intervals using the log-Pearson Type III analysis (Reference 10), as <br />outlined in Bulletin 17B (Reference 11), and using the HEC-FFA computer model <br />(Reference 12). In addition, to supplement the gage data, other sources of flood <br />information were sought. To determine if the selected stream gages may have been <br />bypassed during larger events, local agencies and individuals were contacted for <br />supporting information. The additional information, when available, was included in <br />the gage analysis. For example, during the 1997 event on the Elk River near Milner, <br />roadway overtopping was observed by the USGS. Based on the site observations, a <br />flow of approximately 370 cfs was estimated to overtop the roadway. <br /> <br />23 <br />