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<br />. <br /> <br />nnr<''7rl1 <br />, ~ ~ j ~_~ L.-~ <br /> <br />. <br /> <br />PART VB. IUSTORlC FLOWS OF THE ANIMAS RIVER <br /> <br />. <br /> <br />Four USGS gaging stations have been utilized along the mainstem Animas <br /> <br />River. The HowardsviUe gage is located at the headwaters of the river near <br /> <br /> <br />Silverton, so the records at this site are of no value in estimating historic and <br /> <br /> <br />virgin flows in the lower Animas River area in the Durango area. The Tacoma <br /> <br /> <br />gaging station located 16 miles north of Durango has period of record dating <br /> <br /> <br />from 1946 to 1956. The gages at Durango and near Cedar Hill provide a long-term <br /> <br /> <br />period of record and provide an excellent source of information concerning <br /> <br /> <br />historic flows on the Animas River. <br /> <br />. <br /> <br />. <br /> <br />A description of the river segments or reaches used in the hydrologic <br /> <br /> <br />analysis is presented in Part III of this report. Historic stream flows within <br /> <br /> <br />each reach were estimated through use of the available gage records and through <br /> <br /> <br />estimates of tributary inflows and irrigation and municipal depletions along <br /> <br /> <br />the river. <br /> <br />. <br /> <br />. <br /> <br />Tributary Flow Estimates <br /> <br /> <br />Tributaries to each reach of the Animas River signficantly contribute <br /> <br /> <br />to the overall river flow in response to snowmelt runoff and rainfall events. <br /> <br />Estimates of tributary inflows were made through use of elevation-runoff rela- <br /> <br /> <br />tionships for the San Juan River basin and precipitation records. <br /> <br />. <br /> <br />Figure Z is a graphical presentation of the approximate annual runoff <br /> <br /> <br />generated per square mile, plotted against mean basin elevation, for a number <br /> <br />of gaged drainage basins in the San Juan River basin. Figure Z also includes <br /> <br /> <br />estimates of average annual runoff per square mile for specific tributary areas <br /> <br /> <br />in the Animas River basin. The basic data used in preparing Figure Z is presented <br /> <br /> <br />in Table 8. A summary of the estimated annual runoff for the tributary areas <br /> <br /> <br />in the Animas River basin is presented in Table 9. <br /> <br />. <br /> <br />. <br /> <br />-17- <br /> <br />. <br />