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<br />~, J _ <br /> <br />.' <br /> <br />001466 <br /> <br />3.0 <br /> <br />SITE SPECIFIC ANALYSIS <br />GUNNISON RIVER ABOVE BLUE MESA RESERVOIR <br /> <br />3.1 General <br />With the foregoing portion of this report as a background on the general <br />characteristics of river icing, the remainder is devoted to analysis and <br />evaluation of the specific conditions on the Gunnison River, just upstream <br />of the Blue Mesa Reservoir. In this section of the report, summaries will <br />be presented of previous investigations of the Gunnison River icing <br />problem. Descriptions and a discussion of the observations made during the <br />1984-85 winter, as part of this study, will also be presented. In addition, <br />an analysis has been made of the relationships between the ice jam movement, <br />temperatures, Blue Mesa Reservoir levels, Gunnison River flow and the shape <br />and gradient of the river in the study area. <br /> <br />During the 1 ast two winter seasons (1983-84 and 1984-85), ice jams have <br />formed early in December and moved upstream, past the Dos Rios residential <br />development. The head of these jams advanced and receded with temperature <br />changes and resulted in forcing river flows out of the natural channel at <br />numerous locations. The flooding problems in the region appear to be <br />getting more critical and more severe in recent years. <br /> <br />An attempt will therefore be made to evaluate whether this is a trend or <br />merely a result of the unique conditions of the last two years. <br /> <br />3.2 Previous Observations <br />The most complete record of the ice jam formation and movement in the study <br />area is documented in a report pub1 ished by the U.S. Bureau of Reclamation <br />in 1979, Winter Ice Jams on the Gunnison River. The report (technical <br />report REC-ERC-79-4) was prepared by Mr. Phil H. Burgi, of the Hydraulics <br />Branch of the Bureau's Engineering and Research Center in Denver. In this <br />report, detailed field observations were noted for the winter seasons of <br />1970-71, 1972-73, 1973-74, 1976-77. No reasons were given for selecting or <br />reporting only those particular seasons, although the Blue Mesa Reservoir <br />was filled in 1967. <br /> <br />-11- <br />