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<br />SUMMARY <br /> <br />more stable due to the effects of existing upstream water storage <br />projects. Changes being caused by the Aspinall Unit on the <br />Gunnison River upstream from the North Fork would continue. <br /> <br />With development, more of the riverbed would be exposed. <br />Riparian vegetation would encroach during periods of low and <br />intermediate flows but would be scoured during periods of high <br />flows. <br /> <br />Without development, the Uncompahgre River upstream of the study <br />area would become a narrower and more stable river under the <br />influence of Ridgway Reservoir. Within the study area <br />(downstream from the South Canal), the bank erosion that now <br />occurs would continue. <br /> <br />With development, bank erosion in the uncompahgre River between <br />the South Canal and the proposed tailrace would decrease together <br />with the river's potential to scour encroaching vegetation. <br />Between the proposed tailrace and Delta, the river would become <br />more unstable and significant additional bank erosion would occur <br />unless bank protection was initiated. To minimize this erosion, <br />bank stabilization would be performed in areas found to be most <br />susceptible to erosion before development. Changes in erosion <br />would be monitored during operations, and further bank stabili- <br />zation would be completed where necessary. <br /> <br />Water Quality and Temperature <br /> <br />Under the no-action alternative, water quality in the Gunnison <br />River would not change significantly. Water quality in the <br />Uncompahgre River may improve as Ridgway Reservoir will settle <br />out sediment and other pollutants. <br /> <br />Under the development alternatives, additional diversion from the <br />Gunnison River would reduce the volume of high quality water <br />available to dilute lesser quality tributary inflows. This <br />reduction in water quality would occur primarily downstream from <br />the North Fork. Temperatures in the Gunnison River. would be <br />slightly colder in the winter and warmer in the summer. The con- <br />ditions under which ice forms in the Gunnison River would occur <br />more frequently under the development alternatives. Ice accumu- <br />lation would be most extensive below the North Fork confluence <br />but would also increase above this tributary. Alternative F <br />provides operational changes to decrease diversions and therefore <br />increase flows when ice conditions create environmental problems. <br /> <br />Water supplies in the Uncompahgre River in the 12-mile reach <br />between the South Canal and Montrose would receive less high <br />quality water from the Gunnison River during the irrigation <br /> <br />S - 6 <br />