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Stage Changes And Ice Formation
<br />The pattern of hourly releases from Flaming Gorge Dam has changed substantially from 1988
<br />(Valdez and Masslich 1989, and Wick and Hawkins 1989) to 1993. In February 1988, releases varied
<br />from about 1,000 to 4,000 cfs in patterns that differed considerably between days (Figure 17). For
<br />the days of February 10, 13, and 16, flow pattern varied from a steady release of about 2,000 cfs, to
<br />a prolonged high release of about 4,000 cfs from 8:00 am to 10:00 pm.
<br />For February 8, 10, and 13, 1993 (Figure 18), the pattern was quite different, and was marked
<br />by a higher nighttime release of about 800 cfs, and two daily flow increases to about 1,100 cfs--one
<br />in the morning and one in the evening. The 1993 release scenario had less magnitude of fluctuation
<br />than the 1988 scenario.
<br />Stage changes modeled by Valdez and Masslich (1989) for various locations downstream of
<br />Flaming Gorge Dam indicate that daily flow fluctuations caused by increased releases of 800 to 4,200
<br />cfs for 8-hour duration can fracture substantial ice cover thickness. Using the relationship developed
<br />by Donchenko (1978) (Figure 19) that ice cover is fractured and dislodged by a fluctuation equal to
<br />three times ice thickness, it is calculated that stage changes of 58, 4b, and 15 cm at Mitten Park,
<br />Jensen, and Ouray, respectively, could disrupt ice cover 19, 15, and 5 cm thick at each site,
<br />respectively (Table 5). According to Calkins (1979), greatest thickening of ice occurs in large pools,
<br />at a rate of up to 0.5 m in a 10-day period (5 cm/day). Thus, under maximum ice development and
<br />thickening, the number of days required to achieve ice thickness sufficient to resist disruption from
<br />maximum fluctuation of 800 to 4,200 cfs would be at least 3.8 days, 3.0 days, and 1.0 days at the three
<br />sites, respectively.
<br />Smith and Green (1990) using the SSARR model for peaking release of 800 to 4,200 cfs for
<br />10-hour duration predicted stage changes of 87, 71, and 44 cm at Mitten Park, Jensen, and Ouray,
<br />respectively. These predictions show that high powerplant releases of longer duration are capable
<br />of generating greater stage changes, which could disrupt ice as thick as 29, 24, and 15 cm at the three
<br />sites, respectively.
<br />Under pre-dam flows (Figure 15), one standard deviation from mean daily winter flows (600-
<br />1,000 cfs) was 250 to 300 cfs, or a stage change of 3 to 5 cm, depending on change duration and
<br />distance from the input source. This magnitude of flow change was capable of disrupting ice
<br />thickness of only 1 to 1.7 cm, and probably caused insignificant changes in main channel velocity and
<br />low-velocity habitats such as backwaters.
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