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<br />record from 1946 to 1986. The Golden gaging station was located <br />approximately 21 miles downstream from the Lawson gage from 1911 <br />to 1974 and from 1974 to present is located downstream of the <br />Church Ditch. <br /> <br />HYDROLOGIC ANALYSIS <br /> <br />Methodoloqy <br /> <br />Discharge frequency relationships for Clear Creek were <br />based on a combined-population snowmelt/rainfall discharge <br />frequency analysis. This approach was taken due to the basin's <br />extremely high elevation, 7500 feet to 12,800 feet above mean <br />sea level. Rainfall discharge frequency relationships were <br />estimated using the Environmental Protection Agency's (EPA) <br />storm Water Management Model (SWMM) as modified by the Missouri <br />River Division of the u.s. Army Corps of Engineers. Rainfall <br />runoff modeling was selected for developing the rainfall <br />discharge frequency relationship since infrequent rainfall <br />floods are not inherent in the Clear Creek streamflow records. <br />The snowmelt discharge frequency relationships were determined <br />from an intra-basin regional analysis. The regional analysis <br />was developed for Clear Creek by relating the drainage area to <br />the mean flood logarithm and the standard deviation of the <br />logarithms of the annual snowmelt peak discharges at two gaging <br />stations located on Clear Creek. <br /> <br />Rainfall Discharqe Frequency <br />SWMM Model Confiquration <br /> <br />The Clear Creek basin was divided into 597 subcatchments, <br />which averaged 275 acres per subcatchment. Accumulated point <br />precipitation values at 30-minute, 1-hour, 2-hour, 3-hour, and <br />6-hour time increments were obtained from the NOAA Atlas 2, <br />Volume III - Colorado (USDOC, 1973) for the 2-, 5-, 10-, 50-, <br />and 100-year flood frequencies. To better approximate the <br />values for rainfall events, the May to October series found in <br />NOAA Atlas 2 was used. The 500-year accumulated point <br />precipitation values were determined by extrapolating the 2-, <br />5-, 10-, 50-, and 100-year values. Values for all frequencies <br />were adjusted for depth-area durations prior to application in <br />the SWMM. The maximum 6-hour point rainfall values and adjusted <br />rainfall values are presented in Table 2. Hypothetical storm <br />distribution for each frequency is listed in table 3. <br /> <br />3 <br />