Author(s): Fred E. Parkinson
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Abstract: Field studies have been carried out over the winters 1979-80 and 1980-81 to define the winter regime in the lower Liard River and in the Mackenzie River from their confluence at Fort Simpson downstream to the Beaufort Sea. The total river length studied is 1820 km. 45 coloured slides were presented to show the main characteristics of the ice covers that were observed over the two winter seasons. The commonest formation mechanism found during freeze-up was development of wide shorefast columnar ice sheets out from both shores. Final closure of the remaining main channel was generally by build-up of an accumulation cover. In steeper reaches, shore to shore accumulation covers were noted, and in continuous rapids sections, anchor ice projections up from the riverbed facilitated closure by accumulation. Evolution of the cover during the coldest winter months was a gentle process involving progressive thickening of the thermal cover. Only a few small open water patches remained in locations with local high velocities. Two completely different break-up sequences were observed. The first was a low discharge case where the ice melted in situ, with virtually no ice jam development. The second occurred as a result of a heavy storm in the headwaters that sent a rapid runoff wave through the whole system, creating near-flood level ice jams.
Year: 1981