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<br />. <br /> <br />To determine appropriate infiltration rates for the upper watershed above Bayfield, the <br />Albuquerque District generated a HEC-l watershed model for Bear Creek, a 19,3-square-mile <br />tributary to the Los Pinos River in La Plata County. To simulate a critical storm, the rainfall in the <br />Bear Creek HEC-l model was reduced for the 19-square-mile drainage area of Bear Creek, The <br />frequency-discharge peaks computed by the Bear Creek HEC-l model were calibrated to peak <br />discharges calculated for Bear Creek from the USGS regional equations by adjusting the infiltration <br />rates, <br /> <br />Based on this analysis, the Albuquerque District adopted the calibrated infiltration rates to <br />apply to the HEC-l model for the approximately 70-square-mile Los Pinos River watershed upstream <br />ofBayfield, The infiltration amounts for the upper watershed for each frequency are listed in Table 2, <br /> <br />To determine infiltration rates for the remaining Los Pinos River watershed downstream of <br />Bayfield and upstream of the Colorado-New Mexico state line, the Albuquerque District developed a <br />HEC-l watershed model for Spring Creek, a 58-square-mile tributary to the Los Pinos River in the <br />Southern Ute Reservation, The rainfall in the HEC-l model was reduced for the 58-square-mile <br />drainage area of Spring Creek to simulate a storm critical to that watershed, The discharge-frequency <br />peaks computed by the Spring Creek HEC-l model were calibrated to peak discharges calculated for <br />Spring Creek from the USGS regional equations by adjusting the infiltration rates, <br /> <br />. <br /> <br />Based on this analysis, the Albuquerque District adopted the calibrated infiltration rates to <br />apply to the remaining 230-square-mile watershed downstream ofBayfield, The infiltration amounts <br />for the lower watershed for each frequency are listed in Table 2. <br /> <br /> TABLE 2 <br /> INFILTRATION RATES <br />FREQUENCY Initial Loss Rate Above Initial Loss Rate Below Uniform Loss Rate for <br /> Bayfield Bayfield Entire Watershed <br /> (Inch/Hour) (Inch/Hour) (inch/Hour) <br />1O.0%-Chance (lO-year) 1.035 0.92 0.30 <br />4.0%-Chance (50-year) 1217 1.075 0.30 <br />2.0%,Chance (IOO,year) 1.340 1.171 0.30 <br />1.0%,Chance (lOO'year) 1.379 1.182 030 <br />O,2%-Chance (500-year) 1.435 1.182 0.30 <br /> <br />. <br /> <br />5 <br />