Supercooling in Rivers: Field Measurements and Surface Energy Budget Analysis

• Author / Creator

  Boyd, Sean Ryan

• The process of supercooling, where turbulent water is cooled below freezing while remaining a liquid, is a necessary condition for the formation of frazil and anchor ice in northern rivers during the late fall and winter. While the phenomenon has been often investigated in laboratory, relatively few studies report field observations. This thesis reports on 696 supercooling events recorded on three regulated Alberta rivers from 2015 – 2020. These supercooling events were analyzed for properties including peak supercooling temperature and duration, and analyzed in order to increase our understanding of the behaviour of supercooling in rivers. The median peak supercooling temperature across all events was -0.013oC and a median cooling rate of -2.5x10-4 oC/minute. Though the median event duration was 4.8 hours, events with durations from 2 to 14 days were regularly observed, exceeding the longest events previously reported in literature of ~50 hours. Preliminary analysis of longitudinal gradient of supercooling events in rivers showed the potential impact of both dam regulation and urbanization on spatial distribution of supercooling. Comparison between the behaviour of supercooling on left and right bank in one river showed differences in frequency and duration of supercooling events cross channel, which may have additional implications for the spatial distribution of frazil ice production.

  Since supercooling events are driven by climate factors of the late fall and winter, understanding the heat fluxes at the water surface and how they drive supercooling is crucial to improving understanding of supercooling. Supercooling data collected on two rivers for the 2016-2017 season was analyzed along side local weather data to provide insight into the relationship between supercooling events and the local surface energy budget. From the calculated shortwave, longwave, sensible, and evaporative heat fluxes, it was found that the shortwave and longwave were the dominant heat fluxes during supercooling events, with 97.4 % of events predominantly warmed by shortwave radiation, and 80.0 % of events predominantly cooled by longwave radiation. Sensible heat flux was found to primarily be a secondary heat flux unless air temperature dropped significantly colder that the season average (average air temperature -14.8 oC during supercooling compared to the season average of -8.99 oC during supercooling). Evaporative heat flux tended to be negligible unless air temperature was positive along side high wind speeds and low magnitude radiative heat fluxes. While no linear correlation was found between supercooling parameters and event averaged heat flux components, it is clear from the analysis that the start and end of supercooling events are notably impacted by the diurnal cycling of shortwave radiation.

• Subjects / Keywords

  • Supercooling
  • River ice processes
  • Frazil ice
  • Energy budget

• Graduation date

  Spring 2022

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-wyvc-9p56

• 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.