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. . . I. INTRODUCTION Purpose The purpose of this report is to present the methodology and results of the hydrologic analyses for the upper Clear Creek drainage basin in Clear Creek County, Colorado, Study results include computed peak discharges for the 2-, 5-, 10-, 50-, 100-, and 500-year flood frequencies for selected locations on Clear Creek, South Clear Creek, West Fork Clear Creek, Chicago Creek, and the Fall River. Authority According to Section 37-60-106(l)(c) of the Colorado Revised Statutes, the Colorado Water Conservation Board has the power and duty: ... "to devise and formulate methods, means, and plans for bringing about the greater utilization of the waters of the state and the prevention of flood damages therefrom, and to designate and approve storm or floodwater runoff channels or basins, and to make such designations available to legislative bodies of cities and incorporated towns, to county planning commissions, and to boards of adjustment of cities, incorporated towns, and counties of this state".... Acknowledl!ments This report and the analyses described herein are reVISIOns to the "Engineering Division Technical Report, Hydrologic Analysis, Type 15 Flood Insurance Study, Clear Creek County, Colorado, Final Report" dated September 1990 as prepared by the V,S, Army Corps of Engineers, Omaha District. The background information contained in the Corps report was utilized for this report, Hydrologic information and peak flow values contained in the 1990 Corps report for Clear Creek from Lawson downstream, Mill Creek, and Soda Creek have not been superseded by this study, II. BACKGROUND INFORMATION Basin Description The study area includes the uppermost portion of the Clear Creek basin from the Continental Divide to the gaging station located near Lawson, Colorado, Clear Creek flows east from the Divide through Silver Plume, Georgetown, and Lawson. The Creek continues to flow in an easterly direction through Idaho Springs, Golden, and the Denver Metropolitan area where it empties into the South Platte River. The drainage area above Lawson covers approximately 145 square miles. Overland slopes vary from 10 percent in the lower basin to over 80 percent in the high elevation mountainous regions of the upper basin, The four major tributaries to the Clear Creek study area are South Clear Creek, West Fork Clear Creek, Fall River, and Chicago Creek. Clear Creek channel slopes vary from 0,21 ft/ft in the upper basin, to about 0.016 ft/ft near Lawson. Figure 1 presents a basin map for upper Clear Creek that was prepared by the Corps.