Author(s): Sean Boyd; Tadros R. Ghobrial; Mark R. Loewen
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Abstract: Supercooling events occur in northern rivers when the turbulent water is cooled below the freezing point. This leads to the formation of frazil ice crystals in the water column and/or anchor ice formation on the bed. The heat flux at the air-water interface and the latent heat released by ice formation are the dominant factors controlling the water temperature. If the air-water heat flux is approximately constant the water temperature decreases until it reaches a peak supercooling value, then it increases and eventually reaches a stable value slightly below zero called the residual temperature. At this time the heat being lost through the airwater interface is balanced by the heat being added by frazil or anchor ice formation. However, because the air-water heat flux is typically not constant due to changing environmental conditions the relationship between the water temperature and ice generation is likely more complicated. There are very limited measurements of supercooling in rivers reported in the literature. In this study field measurements were made in three rivers in Alberta, Canada (Kananaskis, North Saskatchewan, and Peace Rivers) over several winters using precision water temperature loggers (accuracy ±0.002 0C). The loggers were mounted in metal casings and anchored to the riverbed. The temperature time series were used to compute the characteristics of supercooling events including the timing, duration, and peak supercooling temperature. The characteristics of these events are analysed to determine significant patterns and trends within the data across all three rivers, and within each river. These patterns are compared to the recorded climate conditions from nearby weather stations such as solar radiation, air temperature and relative humidity.
Year: 2020