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<br />. <br /> <br />t][P OS? <br />," <br /> <br />. <br /> <br />Based on examination of the river basin characteristics, it was concluded that <br /> <br />the Mancos River (from Weber Canyon to Highway 666) and the La Plata River <br /> <br /> <br />(from ChelT)' Creek to the State Line) have virgin streamflow conditions that <br /> <br /> <br />are very similar to that of McElmo Creek. Therefore, the virgin streamflow <br /> <br /> <br />of McElmo Creek was estimated to be an annual average of 25 acre-feet per <br /> <br /> <br />square mile of drainage area. This estimate was further refined as follows, <br /> <br /> <br />based on the variation of elevations within the McElmo Creek drainage basin: <br /> <br />. <br /> <br />. <br /> <br /> Average Annual <br /> Drainage Mean Mean Virgin <br /> Area Precip. Basin Runoff <br />River Segment ( sq-mi) (inches) Elevation (ac-ft/sq-mi) <br />McElmo Creek above 147 15 6600 30 <br />Alkali Canyon <br />Alkali Canyon to "McElmo 136 13 6500 25 <br />Cr. below Cortez" gage <br />"McElmo Creek below 63 11 5800 20 <br />Cortez" gage to state <br />line <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />Short-Term Runoff <br /> <br /> <br />Gaging station records for McElmo Creek and other streams in the general <br /> <br /> <br />area indicate that a large portion of the total annual streamflow occurs as short <br /> <br /> <br />duration-high volume runoff events. Since runoff from short-term events is <br /> <br /> <br />very sporadic, it may be impractical to design irrigation or industrial diversion <br /> <br /> <br />facilities to divert much of this flow. Therefore, an analysis was performed <br /> <br /> <br />to identify the portion of the total annual streamflow that is associated with <br /> <br /> <br />short-term runoff events. Separate monthly summaries of McElmo Creek virgin <br /> <br /> <br />flow were prepared, both with and without the inclusion of short-term runoff. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />The virgin flow of McElmo Creek is dependent on rainfall within the <br /> <br /> <br />drainage basin and is particularly affected by extreme precipitation events. <br /> <br /> <br />Daily precipitation records for Cortez, located near the center of the McElmo <br /> <br /> <br />Creek drainage basin, are available throughout the 1951 through 1980 study <br /> <br />. <br /> <br />-15- <br /> <br />i,L_k~ <br />