Measurements and Analyses of Velocity Profiles and Frazil Ice-Crystal Rise Velocities During Periods of Frazil-Ice Formation in Rivers

Abstract

The vertical concentration distribution of frazil-ice crystals in a stream during the formation and gro~lth of frazil ice was discussed in a preliminary way by Gosink and Osterkal!1p (1981). This paper extends and completes the analysis of buoyant rise velocities of frazil-ice crystals and applies the results to an interpretation of measured velocity profiles in rivers during frazil-ice events. Additional experimental data are also presented. Two tillle scales are defined: the buoyant time scale TB, whi ch represents the time requi red for a frazil crystal to rise, huoyantly, from the river DOttOI!1 to the water surface, and the diffusive time scale TO, which represents the time required for a frazil crystal to be transported by turbulence through the de[lth. It is shown that the ratio of the time scales TB/To defines the nature of the layering processes; in particular, if TB/To<1, then buoyant forces ~ill lift a frazil crystal faster than turbulent diffusion can redistribute it and the f10\'/ will be layered. Conversely, if TB/TO>1, turbulent mixing will proceed faster than buoyant 1 ifti ng and the fl ow ~Ii 11 be well-mixed. This ratio, for frazil particles of di arneter 2 i"l1I11 or more, corresponds to rul e-of-thumb velocity criteria developed in Non'lay and Canada to di sti ngui sh 1 ayered frazi l-i ce/l'later fl O~I froi"1 wellmixed flow.The development of this theory depends in large part upon the deterr.lination of TB, which depends upon the rise velocity of frazil-ice crystals. A force ba 1 ance ,node 1 was developed for the ri se velocity of a frazil crystal. Field observations during frazilice formation in Goldstream Creek and in the Chatanika River north of Fairbanks are reported, including a series of measure~ents of the rise velocities of frazi1-ice crystals. Typical particle size of frazi1 ice was about 2 n~ with a rise velocity of about 10.0 mm S-I. The agreement of measured rise velocities with the theoretical model is good considering uncertainties in the drag coefficient and in the deterlllination of frazil crystal sizes under field conditiolls.Velocity profiles in the Chatanika River and in Soldstream Creek during frazil formation suggest that the time-scale ratio may serve as a transition criteri 011 betv/ee'l 1 ayered frazil-i ce/water flow and \~ell IIlixed flow. This ratio was calculated with the rise velocity of frazil-ice crystals arbitrarily chosen to be 0.01 m s-l. I >.JTRODUCTI ONObservations of ice formation in northern rivers during the freeze-up period show that three ice-flo\~ regimes are common: sheet ice, floating frazil ice and a well-mixed flow (frazil-ice crystals and water). In the last case, if the velocity of the river is sufficiently high, open water conditions may persist throughout the winter.Designers of hydraulic structures such as canals, water transportation facilities, hydroelectric power structures, water-intake structures, etc., may require inforMation on which flow regime to expect under a given set of flow conditions and on the transition from an ic...

A model of marine ice formation within Antarctic ice shelf rifts

“…This clearly portrays how small the volume of the plume is relative to that of the cavity. The velocity of the plume at the top of the cavity is 2.54 cm/s, which is much higher than the rise velocity of the crystals (2 mm/s, calculated along the lines described by Gosink and Osterkamp [1983]), justifying the assumption that the crystals are carried along with the plume until it reaches the top of the rift. Also, Figure 5 illustrates the profile of the rift's wall halfway through the integration and at its end.…”

Frazil dynamics and precipitation in a water column with depth-dependent supercooling

“…S i represents the interaction terms between class i and other frazil size classes and therefore is a component of the release or uptake of water owing to the phase changes represented by the final term on the right-hand side of (2.4). The frazil rise velocity w i relative to the moving fluid is approximated by frazil's buoyant drift velocity in still water (Gosink & Osterkamp 1983): 8) where g = 9.81 m s −2 is the magnitude of acceleration due to gravity, a r is the aspect ratio of a frazil disk and r i is its radius. In this expression C d i is the crystal drag coefficient, which is calculated iteratively from the disk Reynolds number (JB).…”

Hydraulic and Physical Properties Affecting Ice Jams

“…Gosink and Osterkamp (1983) reported frazil particle diameters ranging between 1 and 6 mm during a series of tests on the Chatanika River, Alaska. Chacho et al (1986) reported frazil diameters of 5 mm to 150 mm in the Tanana River.…”