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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />14!:H <br /> <br />The average annual virgin flow of the Mancos River watershed above <br /> <br /> <br />Navajo Canyon (Point 18 on Figure D-ll) estimated by W.W. Wheeler & <br /> <br /> <br />Associates, Inc., is nearly six times the average annual irrigation <br /> <br /> <br />water requirement. However, in an average year, the runoff starts <br /> <br /> <br />in mid-April and is essentially over by the end of June. In most <br /> <br /> <br />years the late-season streamflows in the Mancos River watershed are <br /> <br /> <br />inadequate to supply the irrigation water requirements for the <br /> <br /> <br />initially identified PIA lands. Table D.7 indicates the months <br /> <br /> <br />(encircled) when the virgin flows during the 30-year historical <br /> <br /> <br />study period at the confluence with Navajo Canyon would have been <br /> <br /> <br />insufficient to supply the initially identified PIA. The virgin <br /> <br /> <br />flows listed in Table D.7 have not been adjusted for the estimated <br /> <br /> <br />stream losses due to phreatophytes. Considering stream losses, the <br /> <br /> <br />months of shortages would have been even greater. A full supply for <br /> <br /> <br />all of the initially identified PIA lands could have been obtained <br /> <br /> <br />from the river without regulation in only two years, 1957 and 1965. <br /> <br /> <br />It is apparent that regulation of the natural streamflows of the <br /> <br /> <br />Mancos River by storage in a reservoir will be necessary to provide a <br /> <br /> <br />full irrigation supply for the PIA lands. In all but one year (1977) <br /> <br /> <br />the ?torage would be required for annual regulation of the runoff, <br /> <br /> <br />not for long-term carry-over. <br /> <br />D.4.6 Potential Storage Sites <br /> <br /> <br />Since the new PIA parcels to be supplied are all located along the <br /> <br /> <br />mainstem it was assumed the most cost effective arrangement would be <br /> <br /> <br />to deliver the augmentation supplies from storage via releases to the <br /> <br />19 <br />