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<br />SUMMARY
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<br />STREAMFLOWS
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<br />Under the ~o-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, '
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<br />With alterrtatives 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'/sexcept during extremely dry periods, However,
<br />diversions from the river would increase, with the greatest
<br />increase oc;curring 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,
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<br />Average December through February flows entering the Black Canyon
<br />would be 1,392 ft'/s for alternative A, 476 ft'/s for S, 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 for F.
<br />Minimum streamflows would be 300 ft'/s for all alternatives, but
<br />the frequency of 300-ft'/s flows would increase significantly with
<br />development alternatives,
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<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.
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<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 S, 364 percent for alternative C, 318 percent for
<br />alternative E, and 336 percent for alternative F.
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<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) .
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