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<br />. <br /> <br />fHlHISl <br /> <br />. <br /> <br />B. <br /> <br />. <br /> <br />C. <br /> <br />. <br /> <br />D. <br /> <br />. <br /> <br />Since the Mancos River drainage basin is adjacent to the McElmo <br /> <br />Creek drainage basin, the estimated pattern of river gains in <br /> <br /> <br />the lower areas of the Mancos River drainage basin is comparable <br /> <br /> <br />to the monthly pattern of streamflow entering McElmo Creek. <br /> <br />Precipitation records for Cortez were compared with the daily <br /> <br /> <br />flow records of McElmo Creek at the state line gage to identify <br /> <br /> <br />periods of high streamflow associated with short-term precipitation <br /> <br /> <br />events in the basin. <br /> <br />Riparian vegetation along McElmo Creek is a significant factor <br /> <br /> <br />in depleting the natural streamflow of McElmo Creek. An estimate <br /> <br /> <br />was made of losses associated with consumptive use by phreato- <br /> <br /> <br />phytes. <br /> <br />. <br /> <br />A detailed description of the virgin streamflow analysis for McElmo Creek <br />is provided below. <br /> <br />McElmo Creek Streamflow - Annual Analysis <br /> <br /> <br />An estimate of average annual virgin streamflow in McElmo Creek was <br /> <br /> <br />made through use of streamflow estimates for other similar rivers in the area. <br /> <br /> <br />Since drainage basin characteristics vary for each river, comparisons can best <br /> <br /> <br />be made in terms of average annual streamflow per square mile of drainage <br /> <br />basin area. Drainage basin elevation must also be considered because of the <br /> <br /> <br />strong orographic effects on precipitation and streamflow at higher elevations. <br /> <br /> <br />There are gaging stations in other drainage basins in the general vicinity of <br /> <br /> <br />McElmo Creek that have similar basin characteristics, but these gaging stations <br /> <br /> <br />do not reflect virgin streamflow conditions. An analysis was made of gage <br /> <br /> <br />records, historic irrigation practices, and drainage basin characteristics in the <br /> <br /> <br />Mancos, La Plata, and Piedra River drainage basins, as described in the 1986 <br /> <br /> <br />and 1987 "Hydrology Analysis" reports for these rivers by W. W. Wheeler and <br /> <br /> <br />Associates, Inc. A summary of river basin characteristics is presented in Table 8. <br /> <br />, <br />I. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />-14- <br />