A hydrological analysis of icing formation /

• Main Author: Hu, Xiaogang.
• Other Authors: Pollard, W. H. (advisor)
• Format: Thesis
• Language: English
• Published: McGill University 1996
• Subjects: Aufeis > Cold Regions > Mathematical models; Heat budget (Geophysics) > Cold regions; Ice on rivers; lakes; etc; Arctic; Subarctic
• Online Access: http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=42054

Icings are common hydrological phenomena in arctic and subarctic regions. Their bodies are made up of the accumulation of ice layers formed by the freezing of overflow water during the winter season. Icing formation is a process involving a complex system of thermodynamics and hydrodynamics. In this thesis, the formation mechanics of river icings and ground icings are studied in terms of both thermal and hydrological processes. The energy exchange systems during icing layer formation involve two ice water interfaces and some intra-layer water flow. Using energy balance analysis, this research finds that the outgoing energy components can be ranked according to their importance, with sensible heat being the most important component, radiation heat loss being of secondary importance, and latent heat loss being the least important factor. Further, this research illustrates that the heat conduction between the underlying ice and a newly formed icing layer is time dependent. For example, during the first half cycle of icing layer formation, heat is conducted into the underlying ice, but during the second half of the cycle the heat is conducted in an opposite direction. During icing layer formation, the energy input is supplied mainly by water and incoming solar radiation. Intra-layer running water provides a significant amount of energy when air temperatures are milder, but its significance decreases when air temperatures become colder. Solar radiation during the day may also play an important role in the energy supply regime. River icing formation involves several hydrological processes. The location of a river icing is basically controlled by the channel slope. The damming effect of icing mass plays a significant role in the extension of the icing body, especially in the upstream direction. River icings grow slowly, and generally experience three stages of development, namely the 'freeze-up' stage, 'obstruction' stage and 'overflow' stage, the third stage dominating icing growth. The formation of each icing layer is virtually a small-scale reproduction of these three stages. The model simulation shows that the thickness of icing accumulation increases with an increase in the initial water depth in the channel, but simulation also shows that there is a limiting threshold. The thickness of icing accumulation decreases when the initial channel water depth exceeds this threshold. The growth of an icing is an event-dominated discontinuous process. Even during one icing layer formation, simultaneous growth occurs only within a very limited distance. At a specific location, icing growth is related temporally only over a short period of time. As a discontinuous process, icing spreading and thickening during an overflow event depends entirely on the climatic and topographical conditions. Even though icing layering is influenced by many variables, under small discharge rates, as in the case of ground icing growth, statistical analyses show that the mean spreading length of an overflow event can be described efficiently by five variables: discharge, the temperature of the water, the product of air temperature and wind speed, air temperature and the icing surface slope previous to overflow. The maximum spreading length, however, may only be controlled by four variables: discharge, water temperature, air temperature and the product of air temperature and wind speed. Under field conditions, when wind speed is not measured, this wind related variable may be dropped with only a small decrease in confidence level.