Author(s): Graham K. Holder
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Abstract: The roughness of the underside of a river ice cover is known to undergo several changes during the course of a winter. Typically at the onset of freeze-up, there is a marked increase in hydraulic resistance as ice is formed on the surface. This is followed by consolidation and a general smoothing of the cover bottom during the winter months and the roughness gradually diminishes. As the break-up period approaches, warmer water produces ripples at the bottom of the cover and the roughness increases again before returning to open water values. The increase in roughness may be significant if ice jams fonn during the break-up period. At the interface of the bottom of the ice cover and the flowing water, an exchange of heat occurs. If the air is cold enough and the flux negative, the ice sheet will continue to thicken even if the bulk water temperature is slightly above freezing. However, if the air temperature is above a certain threshold, the warm water under the cover will begin to melt the ice. The main concern of studies undertaken to date is determining the heat transfer coefficient C. While the heat transfer coefficient at the ice-water interface is believed to vary during winter as a function of the ice cover roughness, its variation is difficult to determine due to the physical constraints of obtaining accurate field measurements. The object of this paper is to review some of the work done by others on the subject and compare the proposed relationships with field measurements. A relationship is then proposed that allows the temporal variation in the heat transfer coefficient to be calculated throughout the winter period, with limited field data. Application of the derived relationship to a field case is then presented.
Year: 1996