Author(s): Steven F. Daly
Linked Author(s): Steven F. Daly
Keywords: No keywords
Abstract: Michel’s provocative statement in 1963 that “the phenomenon of frazil…is similar to the more general one of crystallization in a supersaturated medium” led eventually to Frazil Ice Dynamics (Daly, 1984). Frazil Ice Dynamics was the development of a comprehensive, quantitative model of the process of frazil ice formation by relating knowledge of industrial crystallization to the conditions present in natural water bodies. This model provided a framework for addressing the basic questions surrounding the first phase of frazil ice formation: where does the ice come from? How do the crystals grow? Can we predict the form of the crystal size distribution as a function of time and space? These are important questions, but not the only questions. One of the chief characteristics of frazil is it continuous evolution of form. Frazil rarely remains as a collection of isolated, disk-shaped crystals suspended in a turbulent fluid for long. The influence of gravity, the geometry of the waterbody, the level of turbulence, the meteorological conditions, and the inherent physics of ice all cause the ice to evolve in form. In general, the tendency is for frazil crystals to join together and form larger and larger units. However, this tendency is not linear or continuous, and at this point, not well described. In the presence of supercooled water, frazil crystals seem to readily join together to form flocs and when deposited, to form anchor ice. Later, when the water temperature has returned to the equilibrium temperature, frazil crystals, often in the form of slush at the water surface, display only a weak tendency to join together. They can remain as slush for long periods of time, and travel long distances, only slowly forming pans and larger floes. Does our understanding of ice sintering help to explain these observations? New instrumentation has provided new and often startling observations of frazil in suspension in rivers, but the results also highlight the complexity of the formation process. Finally, although our understanding of frazil may not be complete, there are many important, practical problems caused by frazil that need to be addressed. The impacts on water intakes in lakes and rivers during periods of frazil formation are reviewed as well as the practical responses for detection and mitigation.
Year: 2008