Predicting Dynamic River Ice Processes

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River ice is an important issue in Canada, as in many other northern countries. Contrary to the peaceful image that the typical mid-winter ice cover implies, river ice is actually comprised of a broad variety of dynamic processes, particularly during freeze-up and breakup, and these dynamic ice processes can cause significant problems. For example, in the fall as water temperatures cool to a few hundredths of a degree below zero, "frazil ice" particles form. These tiny ice particles are initially suspended throughout the river flow by fluid turbulence. However, frazil behaves in a very 'sticky' manner in this supecooled water and readily sticks to itself and many other objects. It can attach to screens and trash racks on water intakes, cutting off the water supplies to municipalities, industries, and power plants. It can also stick to the river bed, building up "anchor ice", which can be very harmful to fish. For example, in small rivers, anchor ice can fill up the entire channel in a single night, inhibiting habitat access for juvenile fish or blocking the oxygen supply to eggs buried in the stream bed. River ice can be equally problematic in spring. On rivers where the breakup is particularly dynamic, ice jams can form causing flooding and presenting a significant threat to human safety.