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<br />0024 n <br /> <br />Table 17. Relative performance of four augmentation scenarios in reducing flow deficits <br /> <br /> % Reduction of Current Deficits % Reduction of Future Deficits <br />Augmentation Criteria <br />(differential, skew, rate) Dry Mod. Dry Average Dry Mod. Dry Average <br />80 cfs, +25%, 70 cfs 72% 92% 28% 66% 79% 41% <br />80 cfs, +25%, 55 cfs 71% 92% 35% 70% 79% 44% <br />60 cfs, +25%, 50 cfs 71% 95% 52% 71% 90% 65% <br />60 cfs, +25%, 33 cfs 60% 79% 54% 63% 81% 65% <br /> <br />The best performances in each hydrologic category are highlighted in Table 17 (bold typeface). <br />One of the four scenarios above (bold typeface) was marginally better than the other three and was <br />selected to evaluate a variety of augmentation water supply alternatives with the CRDSS. The <br />selected scenario applied the following augmentation criteria: Differential, 60 cfs; Skew, +25%; <br />Augmentation rate, 50 cfs. These criteria produced lower thresholds of 78 cfs in summer (July- <br />October) and 109 cfs in winter (November-February) and upper thresholds of138 cfs in sununer and <br />169 cfs in winter. These criteria determined when and how much water should be delivered from <br />one or more sources (Table 18). A series of simulations with the CRDSS were used to assess the <br />relative ability of one or more sources to satisfy net deficits and quantify impacts on any reservoir(s) <br />from which water was delivered. Using the same augmentation scenario, streamflow augmentation <br />"demand" (in AF/month) was calculated and entered into the CRDSS as a contract delivery from <br />storage. At a nominal augmentation rate of 50 cfs delivered at Maybell, an augmentation water <br />supply of7,000 AF/year would provide about 116 AF/day (99 AF/dayplus a 17-AF allowance for <br />transit losses) for a maximum of61 days. The number of days augmentation would be called for <br />during each CROSS month and year is presented in Table 19. <br /> <br />I <br />I <br /> <br />Tables 18 and 19 show only those 44 years during which some augmentation was required by the <br />selected augmentation protocol. Ifaugmentation water supplies were unlimited, 71 % ofthe average <br />annual augmentation demand would occur from July I through September 30, peaking in September <br />(42%), with only 29% of the demand from November 1 through February 28. If augmentation <br />supplies were limited to -7,000 AF, the percent of volume used from July through September would <br />increase to 72% (September, 41%) with the volume used after September declining an average of <br />only 58 AF, or 14% of demand during the post-September period. The shaded cells in Tables 18 <br />and 19 indicate those months in which all or a significant portion of augmentation demand was not <br />met because available augmentation water supplies had been exhausted in previous months. <br />Augmentation demand exceeded supply in 5 years, of which only 3 years had shortages greater than <br />1,000 AF. Shortages were greatest in September, exceeding 1,000 AF in both years in which there <br />were shortages (1934 and 1977). However, shortages could be mitigated by reducing augmentation <br />rates in these drier years to extend supplies later into the base-flow period. <br /> <br />~ <br /> <br />Management Plan for Endangered Fishes in the Yampa River Basin <br /> <br />39 <br />