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<br />.' <br /> <br />0'0'1 ~ 61 <br /> <br />The record of the movement of the ice jams in the above-noted years, as <br />documented in the USBR report, has been a vital source of information for the <br />ana lys i s contained herein. Reservoi r water 1 evel s, ri ver fl ow records and <br />temperature records are all available from other sources and, for this report, <br />were obtained from those sources. The USBR report, however, is the only <br />record ,and description of the resulting ice jam formation and movement. <br /> <br />The USBR report did identify some important relationships regarding the <br />physical conditions that affect the ice jam formation and movement. The most <br />notable is a statement in the conclusion section of that report: <br /> <br />"The Blue Mesa Reservoir water surface elevation, at the end of <br />November, is an important factor in determining the location of the ice <br />jam head at the start of the winter season. A direct relation was <br />established between this location of the ice jam, and the Blue Mesa <br />water surface elevation. For every additional meter of reservoir <br />elevation, the ice jam started about 280 m farther upstream. In 1970-71 <br />and 1973-74, the jams started out close to Beaver Creek (the highest <br />starting location of the six recorded years) due to relatively high <br />reservoir elevations." <br /> <br />The USBR research al so noted a strong corre 1 at i on between the accumu 1 ated <br />degree days below -lOoC (140F) and the maximum distance upstream of the <br />ice jam movement. The USBR concluded that after the ice cover forms on Blue <br />Mesa Reservoir, the river in the region will also develop an ice cover over a <br />majority of the surface area, following approximately 420 negative degree days <br />below _lOoC. (This is equivalent to a negative 756 degree days below l40F <br />degrees). After such time, the progression of the ice jam is 9reatly <br />diminished or halted because of the lack of frazil ice production. <br /> <br />The data on temperatures and distances in the USBR report are presented in the <br />metric system. Where this information has been used in the analysis herein, <br />conversion to of and distance in feet have been made. <br /> <br />-12- <br />