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<br />nrno;;'] <br /> <br />. <br /> <br />. <br /> <br />PARTVL mSTORIC STREAMFLOWS <br /> <br />. <br /> <br />Although several USGS gaging stations have been established on McElmo <br /> <br /> <br />Creek, only the gage near the Colorado-Utah state line has been in operation <br /> <br /> <br />throughout the 1951 through 1981 study period. As summarized in Appendix A, <br /> <br /> <br />the historic streamflow at the state line gage has averaged 33,300 acre-feet <br /> <br /> <br />per year, with annual flows ranging from about 8,000 to 60,000 acre-feet. <br /> <br />Streamflow of McElmo Creek has been measured at two upstream locations <br /> <br /> <br />since October 1972. Estimates were made of historic streamflow at the upstream <br /> <br /> <br />locations for the years preceding October 1972, based on a comparison of the <br /> <br /> <br />state line stream flows during the concurrent period of record. Historic stream- <br /> <br /> <br />flow of McElmo Creek above Alkali Canyon was estimated to average 15,400 <br /> <br /> <br />acre-feet during the 1951 through 1980 study period, as summarized in Table 1. <br /> <br /> <br />Flows at the "McElmo Creek below Cortez" gaging station site averaged 25,800 <br /> <br /> <br />acre-feet per year, as summarized in Table 2. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />The flow of McElmo Creek in the McElmo Canyon area downstream <br /> <br /> <br />of Cortez is normally adequate to meet the full irrigation requirement for the <br /> <br /> <br />3,000 acres of existing inigated land in the canyon. Shortages occasionally <br /> <br /> <br />occur when return. flows from the Montezuma Irrigation District are insufficient. <br /> <br /> <br />For example, there have been periods of several weeks duration when streamflow <br /> <br /> <br />at the state line gage has been limited to about one cfs, indicating that all of <br /> <br /> <br />the available flow has been utilized at upstream locations. <br /> <br />. <br /> <br />. <br /> <br />It is anticipated that flows in McElmo Canyon will increase by roughly <br /> <br /> <br />4,000 acre-feet per year as irrigation return. flows from the Dolores Project <br /> <br /> <br />enter the stream system. It is not known whether such return. flows will com- <br /> <br /> <br />pletely eliminate periodic shortages in the McElmo Creek area. Potential con- <br /> <br /> <br />struction of the McElmo Creek Unit of the Colorado River Water Quality Im- <br /> <br /> <br />provement Program would have an unknown impact on stream flows, but the <br /> <br /> <br />Unit could possibly result in the loss of roughly 12,000 acre-feet per year of <br /> <br /> <br />irrigation return. flows to McElmo Creek. <br /> <br />. <br /> <br />-12- <br /> <br />. <br /> <br />, <br /> <br />~ ., <br />