Author(s): John R. Marko; Martin Jasek
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Abstract: Results are reported from two annual measurement programs carried out on the Peace River which demonstrated near-realtime capabilities for detailed monitoring of frazil ice particles suspended in the water column using upward-looking acoustic profilers. Prior to local stabilization of the seasonal ice cover, frazil ice was fund to be present only during intervals of measurable supercooling when it was characterized by target strengths uniformly distributed through the middle and upper water column. Ice cover stabilization changed this situation, allowing detection of frazil-like targets at all times but with the upper water column now dominated by the presence of a layer of mobile ice particles associated with target strengths which increased sharply with height. Beneath the stable ice cover, target strength variations in the water column were found to be significantly correlated with both lower frequency variations in regional air temperature and with higher frequency changes in local water levels. Our observations were most consistent with both frazil generation in upstream open water areas and the existence of unknown mechanisms whereby local water level- and/or water speed-dependent processes control the vertical distributions of frazil in the water column beneath the stabilized downstream ice cover. The implications of these results for current models of freezing rivers and for the design of subsequent winter river monitoring and study programs will be discussed.
Year: 2008