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<br />002639 <br /> <br />any biological nexus. Therefore, as a contingency against these uncertainties, Service biologists <br />and hydrologists recommended that a 33 percent buffer be added to the 93-cfs flow target (93 + 31 <br />= 124 cfs) to meet the needs of the endangered fishes from November through February (Table 2). <br />At Maybell, minimum flows of this magnitude or less occurred historically during the winter about <br />1 in 6 years. Modeling based on projections offuture water development and a proposed base-flow <br />augmentation protocol (Roehm 2003) indicates that instream flow augmentation would be needed, <br />to some extent, to satisfy a I 24-cfs winter flow target in an historical context an average of about <br />I in 7 years, whereas some augmentation would be needed from July through August to satisfy the <br />93-cfs flow target an average of I in 2 years. <br /> <br />Table 2. Revised base-flow targets' (cfs) for the Yampa River at Maybell, Colorado <br /> <br />NOV DEC JAN FEB MAR I APR I MAY I JUN JUL AUG SEP OCT <br />124 124 124 124 No flow recommendation 93 93 93 93 <br />Fall-winter base-flow period Spring Runoff Period Per Modde et al. 1999 <br /> <br />, Based on historical frequency, magnitude and duration. There are no specific numerical flow <br />recommendations during spring peak-flow months (March-June). <br /> <br />Imolementation Guidelines <br /> <br />The Service also recognizes that the proposed augmentation protocol and estimated volume of <br />augmentation water supply (up to 7,000 acre-feet (AF) as needed according to the protocol) will not <br />completely satisfy these flow recommendations in the driest 10 percent of years. In these years, <br />7,000 AF of augmentation will only partially satisfy base-flow needs. Based on the proposed <br />augmentation rate of 50 cfs, a 7,000-AF augmentation pool would be exhausted in only 2 months. <br />In such situations, it may be prudent to reduce the augmentation rate and extend the duration of <br />augmentation. For example, reducing the rate to 25 cfs would allow augmentation to continue for <br />4 months. The Service's hydrologist will work cooperatively with the Upper Colorado River <br />Endangered Fish Recovery Program (Program); reservoir operators; the Colorado Water <br />Conservation Board; and Colorado State Engineer to make the best possible use of this limited <br />resource. Other adjustments may be made in the augmentation protocol as deemed necessary and <br />appropriate by the Service and the Program, in consultation with reservoir operators and the State <br />of Colorado. <br /> <br />~ <br />~ <br /> <br />Appendix D - Revised base-flow recommendations for the Yampa River <br /> <br />D-3 <br />