8270 - Laserfiche WebLink

Home Browse Search

movements of stadia rods that had been attached to wooden stands placed on the ice. In addition to measurements of ice distribution and stage changes, field teams spent 23-25 January 1997 measuring ice thickness and channel depth at multiple locations across the river channel at 17 river cross sections under the steady flow regime. These measurements were made by using a hand-operated ice auger to create 5.7 cm holes in the ice cover and a tape measure with a hinged weight to obtain the measurement of ice thickness at each hole following the procedures of White and Zufelt (1994). The water depth at each sample hole was measured with a graduated stadia rod inserted through the hole in the ice. Measurements of ice thickness and channel depth were repeated at the same cross-sections (but using slightly different locations for the holes) on 29-30 January, after the propagation waves from several hydropower peaking cycles had passed through the study area. The locations of the ice measurement cross sections are shown in Figure 3. Because the measurements made at each cross section were considered to be repeated measurements made before and after a treatment (fluctuating flows), mean ice thickness under steady and peaking flows were statistically compared using a repeated measures ANOVA (SAS 1985). In this statistical design, the Type III mean square of the ice thickness measurements within cross sections was used as the error term when testing the hypothesis that the flow regime (i.e., steady releases vs fluctuating releases) affected the thickness of the ice. In the event that stage fluctuations resulting from hydropower peaking caused breakup or downstream movement of the ice cover, ice motion detectors were installed at three locations within the study reach. Each detector consisted of a sensor unit and a wire circuit. Each sensor unit, which contained an internal clock to record the date and time, was installed on the shoreline and the wire connected to the unit was embedded in the ice cover through holes drilled in the ice. The detectors were designed so that any break in the wire, such as would occur if the ice cover moved, would cause the sensor to record the date and time when the circuit was broken. The first ice motion detector was placed at RM 308.2 on 25 January 1997. A second ice motion detector was installed upstream of the Bonanza Bridge at RM 290.4 on 26 January, and a third was installed within the Ouray National Wildlife Refuge at RM 254.3 on 30 January 1997. 2.4 ICE PROCESS MODELING The formation and transport of river ice and the formation of stationary river ice covers can be simulated through the use of numerical models (see for example Lal and Shen 1993; Shen et. al. 1991; Beltaos 1995) and such a numerical ice model (Daly, in prep.) was applied to the study reach of the Green River. This model is composed of a one-dimensional unsteady flow sub-model, a transport sub-model, and an ice cover progression sub-model. Each of the sub-model components are described in the following subsections. In order to understand the influence that the Flaming Gorge Dam release pattern could -9-