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<br />-. <br /> <br />Because of the steep mountain slopes and narrow valleys in Clear <br />Creek County, development has occurred near the streams and often <br />within the floon plain. City streets, state highways, and interstate <br />highways cross the flood plains and often constrict the free-flowing <br />streams with bridges and embankments. Continuing development within <br />the study area is expected, and pressures lea~ing to intensified <br />flood plain use will probably accompany such development. <br /> <br />2.3 Principal Flood Problems <br /> <br />clear Creek flows through Silver Plume in a narrow channel with <br />relatively steep slopes. Large flows through the city are charac7 <br />terized by very high velocities and unstable water-surface elevations. <br />Bridges appear to be the greatest constraints on passage of floodflows. <br /> <br />Flooding in Silver Plume is primarily a function of the spring <br />snowmelt, or possibly snowmelt in conjunction with rain-on-snow. <br />Summer rainstorms do not appear to be the major cause of flooding, <br />although heavy hailstorms occasionally cause drifts of hail that <br />block drainage paths and create some flooding. <br /> <br />A search of newspaper articles and interviews with local citizens <br />revealed that there has been no significant flooding inside the <br />corporate limits of Silver Plume. The only flooding occurred in the <br />vicinity of Cherokee and Gay Streets, when the bridge was over- <br />topped. No definite information as to year, depth, quantity of <br />flow, or exact limits of flooding was available. <br /> <br />2.4 Flood Protection Measures <br /> <br />No flood protection measures are presently in effect in the Town of <br />Silver Plume. <br /> <br />3.0 ENGINEERING METHODS <br /> <br />For flooding sources studied in detail in the community, standard hydrologic <br />and hydraulic stUdy methods were used to determine the flood hazard data <br />required for this study. Floods having recurrence intervals of 10, 50, <br />100, and 500 years have been selected as having special significance for <br />flood plain management and for flood insurance premium rates. The analyses <br />reported here reflect current conditions in the watersheds of the flooding <br />sources. <br /> <br />3.1 Hydrologic Analyses <br /> <br />Hydrologic analyses were carried out to establish the peak dis- <br />charge-frequency relationships for floods of the selected recurrence <br />intervals for each stream studied in detail in the community. <br /> <br />4 <br />