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<br />to be noncontributing to the peak discharge generated from the areas <br /> <br />below each reservoir. A Trilby Lateral crossing in the northwest <br /> <br /> <br />corner of the basin effectively dams a tributary, thereby causing it to <br /> <br />be noncontributing. All pertinent highwsy; county road, and railroad <br /> <br /> <br />structures were evaluated for their temporary flood control potential. <br /> <br /> <br />Reservoir routings utilizing storage-discharge curves were made for 24 <br /> <br />of these structures. <br /> <br />. <br /> <br />MODEUNG STUDIES <br /> <br />GENERAL <br /> <br />The Environmental Protection Agency's Storm Water Management Model <br /> <br /> <br />(SWMM) computer program was used to model rainfall-runoff character- <br /> <br /> <br />istics 0' the Fossil Creek basin. Storms varying in frequency from 10 <br /> <br /> <br />to 500 years were centered over the basin and modeled by SWMM to obtain <br /> <br /> <br />the discharges presented in this report. The SWMM model of the Fossil <br /> <br /> <br />Creek basin contains 161 catchments, 106 streams, reservoir routings <br /> <br /> <br />for 24 road and railroad structures, and a routing for Fossil Creek <br /> <br /> <br />Reservoi~. Basin characteristics for the model were taken from USGS <br /> <br /> <br />7.5-minute quadrangle mapping having a scale of 1:24,000 and a contour <br /> <br /> <br />interval of 10 feet. This SWMM model assumed dams in place, road <br /> <br /> <br />crossings j~ place, and culverts open. <br /> <br />RAINFALL <br /> <br /> <br />Rainfall values for the 10-, 50-, and 100-year, I-hour events were <br /> <br /> <br />obtained from rainfall intensity-duration curves that were developed by <br /> <br /> <br />Resource Consultants, Inc. of Fort Collins, Colorado. These curves <br /> <br /> <br />were derived from data and procedures in Precipitation-Frequency Atlas <br /> <br /> <br />of the Western United States, Atlas 2, Volume III, Colorado, published <br /> <br />by NOAA in 1973. The rainfall intensity-duration curves are shown on <br /> <br /> <br />figure 6. Resource Consultants, Inc. provided a 2-year, I-hour <br /> <br /> <br />rainfall that was obtained from a frequency analysis of 30 years of <br /> <br /> <br />precipitation records at Fort Collins. This rainfall is 0.13 inch <br /> <br />24 <br /> <br />. <br />