CGU HS Committee on River Ice Processes and the Environment 14th Workshop on the Hydraulics of Ice Covered Rivers

When the air temperature begins to drop as winter approaches, surface waters supercool and initiate the formation of ice particles. In a slowly flowing river with a moderate degree of turbulence there exists a vertical stratification which is characterized by a thin supercooled surface layer and a non-supercooled layer of bulk water body. This supercooled surface layer initiates the formation of skim ice particles. In the present study, an extensive laboratory analysis was carried out in the Hydraulics & Research Testing Facility at the University of Manitoba to investigate the behavior, shape and size of these skim ice particles in relation to the flow properties. It was observed that skim ice particles are those ice particles that nucleate on the water surface, in small to moderate turbulent intensities, whenever there is stratification. Four major types of skim ice particle shapes were observed: hexagon shaped particles (including, hexagons, stars and circles), needle shaped particles, leaf shaped particles (including leaf shaped and finger-shaped particles), and irregular-shaped particles. The relative number of each type of skim ice particles and their size in a given flow was observed to be dependent on the degree of turbulence. Surface heat loss has no effect on the shape of the particles. A conclusion was also made regarding the formation of dendrites, bridging and freeze-up. 1