Preprints
https://doi.org/10.5194/tc-2020-212
https://doi.org/10.5194/tc-2020-212

  16 Sep 2020

16 Sep 2020

Review status: a revised version of this preprint was accepted for the journal TC.

Analyses of Peace River SWIPS data and its implications for the roles played by frazil ice and in situ anchor ice growth in a freezing river

John R. Marko and David R. Topham John R. Marko and David R. Topham
  • ASL Environmental Sciences Inc., Saanichton, BC, Canada

Abstract. Peace River SWIPS (Shallow Water Ice Profiling Sonar) data were analyzed to assess and quantify the roles of frazil ice suspensions and riverbed anchor ice grown in situ during the initial buildup of a seasonal ice cover. Data were derived from quasi-continuous monitoring of frazil parameters throughout the water column to provide direct and indirect measures of anchor ice volume and mass growth rates. Analyses utilized water level and air and water temperature information and directly measured acoustic volume backscattering coefficients to track and interpret spatial and temporal changes in riverbed and water column ice constituents. Interests were focused on 4 specific frazil intervals characterized by anomalously low levels of frazil content (relative to simulations with an anchor ice-free river ice model) distinguished by two strikingly different types of time dependences. A simple physical model was proposed to quantitatively account for discrepancies between measured and simulated results in terms of the pronounced dominance of anchor ice as an initial source of river ice volume and mass. The distinctive differences in temporally variable water column frazil content are attributed, in this model, to corresponding differences in the stabilities of riverbed anchor ice layers against detachment and buoyancy-driven movement to the river surface. In accord with earlier observations, the stability of in situ grown riverbed ice layers appears to be inversely proportional to cooling rates. The strength of the coupling between the two studied ice species was shown to be strong enough to detect changes in the anchor ice constituent from variations in water column frazil content.

John R. Marko and David R. Topham

 
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John R. Marko and David R. Topham

John R. Marko and David R. Topham

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Short summary
Acoustic estimates of frazil fractional volume from 4 frazil growth intervals are analyzed with a physical model as a basis for understanding frazil growth in a freezing river. Frazil population changes were found to be tied to contemporary changes in the layers of anchor ice which grow in situ during periods of frazil growth. It is shown that changes in the anchor ice, which is the principal submerged source of river ice, can be most easily tracked by monitoring water column frazil content.