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<br />I) <br /> <br />.. <br />" .. <br />'. <br /> <br />" <br /> <br />INTRODUCTION <br /> <br />PurPose <br /> <br />The purpose of this report is to present the methodology, <br />assumptions, and results of the hydrologic analyses of the upper <br />Clear Creek drainage basin. study results include Clear Creek <br />peak discharges for the 2-, 5-, 10-, 50-, 100-, and SOD-year <br />flood frequencies near Silver Plume, Georgetown, Lawson, and <br />Idaho Springs, Colorado. <br /> <br />BACKGROUND INFORMATION <br /> <br />Basin Description <br /> <br />The study area inclides the uppermost portion of the Clear <br />Creek basin from the )eontinental 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 <br />percent in the lower basin to over 80 percent in the high <br />elevation mountainous regions of the upper basin. The six major <br />~tributaries to the Clear Creek study area are South Clear Creek, <br />West Fork, Mill Creek, Fall River, Chicago Creek, and Soda <br />Creek. Clear Creek channel slope varies from 0.21 ft/ft in the <br />upper 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 <br />comprise the land use in the lower portion of the basin. <br /> <br />I <br /> <br />Climate <br /> <br />The Clear Creek basin is classified as a mountainous <br />highland interior climate. Typical weather for this region <br />consists of cool summers and cold, dry winters. The average <br />temperature is 33 of with extremes ranging from 92 of in June <br />and July to 28 of below zero in January. July and August are <br />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 />1 <br />