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<br />"Precipitation-Frequency Atlas of the Western United States, Volume III, Colorado" <br />(Reference 46). The runoff models were calibrated against the discharge records available at <br />the respective stream gages. <br /> <br />The 10-, 50-, and 1 OO-year peak discharges for Kenneys Run were calculated using the CUHP <br />(Reference 42). The design rainfall data were supplied by the UDFCD based on values <br />obtained from NOAA (Reference 46). Peak discharges at selected locations in the study <br />reaches were obtained by routing the flood hydrographs for each subbasin computed by the <br />CUHP. <br /> <br />The peak discharges for Lena Gulch, upstream of West 6th Avenue, and Jackson Gulch were <br />obtained from a 1975 study done for the UDFCD by Wright-McLaughlin Engineers <br />(Reference 47). In this study, the CUHP was used to calculate the 10-, 25-, and lOO-year <br />discharges for present and future development conditions. The design rainfall used in the <br />study was supplied by the UDFCD, based on information from the NOAA (Reference 46). <br />During the study, the drainage area of Lena Gulch was field checked to determine that current <br />development conditions would be properly reflected by the estimated future development <br />conditions reported in the 1975 UDFCD study. The future development conditions for flood <br />discharge values from the 1975 study (Reference 47) were determined to be valid for this PIS. <br />The 50- and 500-year discharges were estimated from the frequency curves based on the <br />10-, 25-, and 100-year discharge values. <br /> <br />A revised detailed study was prepared for Bear Creek and North Turkey Creek (Reference 8) <br />as follows: <br /> <br />1. Approximately 8.4 miles of Bear Creek, including the reach at Idledale, the reach from <br />Kittredge to Evergreen, and the reach upstream of Evergreen Lake. These detailed study <br />reaches are separated by reaches of approximate study and are therefore noncontinuous. <br /> <br />2. Approximately 6.9 miles of North Turkey Creek, from Danks Drive to the upstream limit <br />of detailed study. <br /> <br />The report by Messrs. Thomas and Miller (Reference 48) recommends mathematical relations <br />for estimating the magnitude and frequency of floodflows on streams draining more than <br />15 square miles in Jefferson County, Colorado. A least square, linear multiple regression <br />analysis defined the recommended relations from data on the floodflow. Physical and <br />climatic characteristics were observed at 27 sample sites in the South Platte River basin in <br />Colorado. <br /> <br />Basic data for the 27 sites were taken from USGS reports. The regression analysis utilized <br />"composite curve" values which were determined by statistically combining individual flood <br />frequency curves of snowmelt and rainfall floods. The regression equations utilize three <br />independent basin parameters: total drainage area, normal annual precipitation, and mean <br />drainage basin elevation. The equations developed in this study may be used to estimate <br />flood peak magnitude and frequency at ungaged sites in Jefferson County with consideration <br />given to their capabilities and limitations. <br /> <br />26 <br />