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3.1 Hydrologic Analyses Hydrologic analyses were carried out to establish the peak discharge- frequency relationships for each flooding source studied in detail affecting the community. A review of flood data and information in the vicinity of Black Hawk for North Clear Creek, Gregory Gulch, and Chase Gulch indicated an insufficient record of measured streamflow to derive the respective floodflow peaks for the various recurrence interval floods. There- fore, a review of regionalized flood jata and other information was conducted to determine the most appropriate means of arriving at the basin flood peaks. The methodologies used, which were developed by the Colorado Wate~ Conservation Board, the U.S. Geolog- ical Survey, the u.s. Soil Conservation Service, and the u.s. Bureau of Reclamation (References 6, 7, and 8), did not produce a consistent or appropriate hydrologic determination for this geographical area. It was decided to use a storm-generated runoff analysis to produce peak floodflows. This involved a determination of the storm precipitation characteristics which, in combination with the soil characteristics, soil moisture content, and ground cover, produced a proper recurrence interval flood. This relationship is simply stated as precipitation (the form or rainfall) minus losses produces runoff or flood peak. This can be represented by a hydrograph depicting floodflow and elapsed time. Precipitation data were derived from publications of the U.S. Weather Bureau and the National Oceanic and Atmospheric Administration (References 9 and 10). The soil moisture and COver conditions used to determine the "losses" were obtained from U.S. Soil Conservation Service mapping and information (Reference 7). Peak discharge-drainage area relationships for North Clear Creek, Gregory Gulch, and Chase Gulch are shown in Table 2. A short-term record of streamflow has been maintained by the U.S. Geological Survey on North Clear Creek near Black Hawk and a longer- term station was in operation on Clear Creek near Golden. The stream gage on North Clear Creek near Black Hawk, 2.3 miles upstream from its mouth, was in operation from 1951 to 1955 and encompassed a drainage area of 55.8 square miles. Gaging station No. 7195 on Clear Creek near Golden was in operation intermittently from 1888 to 1970 and encompassed a drainage area of 369 square miles. Data from these gaging stations were not used in the flood analysis as they contained insufficient information on flood peaks to permit a statiscical a~alysis for projection of floodflows. 3.2 Hydraulic Analyses Analyses of the hydraulic characteristics of flooding from the sources studied were carried out to provide estimates of the eleva- tions of floods of the selected recurrence intervals. 11