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<br />. <br /> <br />001066 <br /> <br />. <br /> <br />an estimate of the overall extent of phreatophytes, but does not provide accurate <br />information concerning the vegetation density and health. <br /> <br />. <br /> <br />The potential consumptive use of water by dense willows, salt cedars, <br /> <br />and small cottonwoods was calculated through use of the Blaney-Criddle method, <br /> <br /> <br />based on experimental data published in "Consumptive Use and Water Require- <br /> <br /> <br />ments in New Mexico," New Mexico State Engineer - Technical Report 30, 1965. <br /> <br /> <br />The net potential consumptive use of alluvial groundwater by phreatophytes, <br /> <br />con-ected for effective precipitation, was estimated to be the following: <br /> <br />. <br /> <br />. <br /> <br /> Potential Potentia I <br /> Consumptive Stream <br /> Use Area Loss <br />Reach (ac-ft/ac) (acres) (ac-ft/yr) <br />Alkali Canyon to site of "McElmo" 3.3 450 1,500 <br />Creek below Cortez" gage <br />"McElmo Creek below Cortez" 3.4 500 1,700 <br />gage to state line gage <br />Totals 950 3,200 <br /> <br />. <br /> <br />. <br /> <br />The open water areas along the La Plata River are typically nan-ow and shallow, <br /> <br />with intermittent flow conditions prevailing during much of the irrigation season. <br /> <br /> <br />The evaporation rate from the wet stream banks and water surface was estimated <br /> <br /> <br />to be roughly equal to the potential consumptive use rate for phreatophytes <br /> <br /> <br />as listed above. <br /> <br />. <br /> <br />. <br /> <br />R,llatively large quantities of return flows began to enter McElmo Creek <br /> <br /> <br />upon development of the irrigation water supply from the Dolores River basin <br /> <br /> <br />in the 1890's. This dependable source of supply to McElmo Creek has probably <br /> <br /> <br />resulted in an increase in the., density and area of riparian vegetation, but no <br /> <br /> <br />estimates are available which reflect the virgin extent of vegetation. For the <br /> <br /> <br />purposes of this analysis, it is assumed that there would be no significant stream <br /> <br /> <br />losses along McElmo Creek under virgin streamflow conditions. In other words, <br /> <br /> <br />it is assumed herein that all of the observed riparian vegetation owes its existence <br /> <br />. <br /> <br />-19- <br /> <br />. <br /> <br />".: ;l"'ll:;; <br />