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<br />,.' <br /> <br />HYDROLOGIC ANALYSIS <br />TYPE 15 FLOOD INSURANCE STUDY <br />CLEAR CREEK COUNTY, COLORADO <br /> <br />I. GENERALINFORHATION <br /> <br />This report discusses the methodology used in describing <br />the hydrologic features of the upper Clear Creek drainage basin. <br />Study results include Clear Creek flows for the 10-year, <br />50-year, 100-year, and 500-year flood frequencies near Silver <br />Plume, Georgetown, Lawson, and Idaho Springs, Colorado. <br /> <br />Basin DescriDtion <br /> <br />The study area includes the uppermost portion of the <br />Clear Creek basin from the Continental Divide to Idaho Springs, <br />Colorado. Clear Creek flows east from the Divide 27.5 miles <br />through Silver Plume, Georgetown, Lawson, and Idaho Springs. <br />The drainage area above Idaho Springs covers approximately 256 <br />square miles (see Figure 1). Overland slopes vary from 10 per- <br />cent in the lower basin to over 80 percent in the high elevation <br />mountainous regions of the upper basin. The six major tributar- <br />ies to the Clear Creek study area are South Clear Creek, West <br />Fork, Mill Creek, Fall River, Chicago Creek, and Soda Creek. <br />Clear Creek channel slope varies from 0.21ft/ftin the upper <br />regions of the basin to 0.017 ft/ft near Idaho springs. <br />Tributary channel slopes vary from 0.6 ft/ft to 0.03 ft/ft. <br /> <br />Land Use <br /> <br />Land use in the upper Clear Creek drainage basin consists <br />mostly of national forests. Mining and some pasture land com- <br />prise the land use in the lower portion of the basin. <br /> <br />II. HYDROLOGY AND METEOROLOGY <br /> <br />Climate <br /> <br />The Clear Creek basin is classified as a mountainous high- <br />land interior climate. Typical weather for this region consists <br />of cool summers and cold, dry winters. The average temperature <br />is 33 degrees F with extremes ranging from 92 degrees F in June <br />and July to 28 degrees F below zero in January. July and August <br />are generally the only frost-free months although frost can be <br />observed at any time of the year, especially in areas above the <br />treeline. <br /> <br />PreciDitation <br /> <br />The average annual precipitation for the upper Clear Creek <br />basin is approximately 14.8 inches with 70 percent of it occur- <br />ring during the 6-month period from April through september. <br />