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<br />II <br /> <br />SUMMARY <br /> <br />STREAMFLoWS <br /> <br />Under the no-action alternative (alternative A), streamflows <br />within the study area would continue to be affected by the <br />operations of upstream reservoirs of the Aspinall Unit and Dallas <br />Creek Project. The Gunnison River would be operated to maintain <br />at least a minimum flow of 300 ft'/s except during extremely dry <br />periods. <br /> <br />With alternatives B, C, E, and F, the Gunnison River would <br />continue to be operated to maintain at least a minimum flow of <br />300 ft'/s except during extremely dry periods. However, <br />diversions from the river would increase, with the greatest <br />increase occurring during the nonirrigation season. Annually, <br />the volume of water in the Gunnison River downstream from the <br />Tunnel would be decreased by 45 percent for alternative B, <br />49 percent for alternative C, 41 percent for alternative E, and <br />44 percent for alternative F. <br /> <br />Average December through February flows entering the Black Canyon <br />would be 1, 392ft'/s for alternative A, 476 ft'/s for B, 471 ft'/s <br />for C, 581 ft'/s for E, and 499 ft'/s for F. Average July through <br />September flows would be 897 ft'/s for alternative A, 730 ft'/s <br />for B,637 ft'/s for C, 730 ft'/s for E, and 730 ft'/s forF. <br />Minimum streamflows would be 300 ft'/s for all alternatives, but <br />the frequency of 300-ft3/s flows would increase significantly with <br />development alternatives. <br /> <br />A monitoring system would be operated to assure that instream <br />flows are maintained and irrigation supplies are protected. <br />As described under alternative F, additional flows would be <br />bypassed to the Gunnison River during winter operations if <br />adverse icing conditions develop. Alternatives E and F also <br />would release up to 1,000 acre-feet of additional flow to the <br />Uncompahgre River via the South Canal during the summer. <br /> <br />The operation of the facility would result in a decrease in <br />Uncompahgre River flows in some reaches and increases in other <br />reaches. Streamflows in the Uncompahgre River entering Montrose <br />would be reduced by 75 percent for all of the development <br />alternatives. Streamflows in the Uncompahgre River downstream <br />from the proposed tailrace would be increased by 339 percent for <br />alternative B, 364 percent for alternative C, 318 percent for <br />alternative E, and 336 percent for alternative F. <br /> <br />Diversions from the Gunnison River would be curtailed under all <br />alternatives, including no-action, during flooding periods along <br />the Uncompahgre River. Under the development alternatives, local <br />flooding and severe local erosion would occur in case of <br />catastrophic penstock failure (an extremely remote occurrence). <br /> <br />S - 8 <br />