The Interaction of Newly Forming Frazil Ice and Sediments

  • Author / Creator
    Hong, Xun
  • In river freeze-up periods, small disc-shaped frazil ice forms during supercooling in turbulent river flow. Under continuous cooling, these particles collide and freeze to form frazil flocs and entrain suspended sediments. Sediment-laden flocs might rise to the surface and freeze into frazil pans, eventually becoming ice cover; or sinking to the bottom and forming anchor ice. Studies of the interaction between newly forming frazil ice and suspended sediments in northern rivers during the freeze-up period are limited. This study investigated how the suspended sediment concentration changes in the water column, which sediment sizes are more likely to get entrained in the frazil ice, and how organic content changes during the supercooling process. To study the sediment concentrations in natural frazil ice, samples were collected from the North Saskatchewan River during the freeze-up period of 2021. Laboratory experiments were done in a freshwater frazil tank in a cold room with three types of sediments (clay-silt, natural, and sand) under three initial concentrations. Samples, including the initial tank water, final tank water, interstitial water, and drained ice, were filtered to examine the sediment concentrations to study the sediment entrainment mechanism.
    Results showed that when frazil ice formed in turbulent tank water, up to 75% of suspended sediments were removed from the water column, even though only 2~3% were entrained in the frazil ice. Based on observations, this is likely because sediment-laden frazil flocs can be shredded by propellers, releasing sediments close to the tank bottom. In addition, the sediment concentrations of the final tank water showed that coarser sediments were removed more efficiently than finer sediments, likely because finer sediments are easier to suspend. Sediments were trapped inside the porous ice lattice of frazil flocs as sediment-laden water flowed through the flocs, like a sieving process. Coarser sediments were more easily entrained in frazil flocs, and finer sediments were more easily flushed out with water, as proven by the ratio of sediment concentrations in the drained ice versus interstitial water 0.7 for clay-silt, 2 for natural, and 3.3 for sand. Sediment concentrations in the field drained ice, and interstitial water samples ranged from 76.7 to 1244 mg/L and 15.1 to 48.9 mg/L. The field's drained ice versus interstitial water ratios (1.8~51) are much bigger than in the lab. Because sediments used in the lab were well-sorted in a specific range, field frazil can entrain small rocks that significantly increase the sediment mass in ice samples. The organic content in river water samples (0.18~0.6) was much higher than tank water samples (0.09~0.13); however, the organic content in drained ice samples from the river (0.05~0.14) and tank (0.1~0.17) was similar to each other, suggesting consistent organic harvesting ability of ice.

  • Subjects / Keywords
  • Graduation date
    Fall 2023
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.