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<br />nOfi371 <br /> <br />. <br /> <br />PART VIII. CALCULATION OF VIRGIN STREAMFLOW FOR <br />LA PLATA RIVER AT HESPERUS 1938-1980 <br /> <br />Since no gage records are available for the confluence of the West, Middle, <br /> <br /> <br />and East Mancos rivers during the 1952 through 1980 period, it was necessary <br /> <br /> <br />to estimate the missing Mancos River flows through use of the La Plata River <br /> <br /> <br />gage. Daily flow records for the La Plata River at Hesperus are available for <br /> <br /> <br />the period of 1938 through 1980, as summarized in Appendix A. Recorded flows <br /> <br /> <br />were affected by diversions upstream of the gage by the following irrigation <br /> <br />ditches: <br /> <br />Ditch Name <br /> <br />La Plata & Cherry Creek Ditch <br />Pine Ridge Ditch <br />Keller Ditch <br /> <br />1938-1951 <br />2,070 <br />1,000 <br />20 <br /> <br />Average Annual Diversion <br />(acre-feet) <br />1952-1980 <br /> <br />2,110 <br />870 <br />70 <br /> <br />. <br /> <br />Totals <br /> <br />3,090 <br /> <br />3,050 <br /> <br />Since these ditches irrigate minimal acreage upstream of the Hesperus <br />gage, the amount of i:rrigation return flows upstream of the Hesperus gage is <br />negligible. See Appendix B for summaries of monthly diversion records. The <br />virgin flow of the La Plata River at Hesperus is equal to the historical flow <br />at the USGS gaging station plus the irrigation diversions that historically bypassed <br />the gage. The calculated virgin flow for the La Plata River is presented in <br />Tables 7 and 8 for the 1938 through 1951 and 1952 through 1980 periods, respec- <br />tively. <br /> <br />. <br /> <br />-25- <br />