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Investigations of Anchor Ice Formation and Release Waves

Author(s): Martin Jasek

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Abstract: BC Hydro owns and operates the W. A. C. Bennett and Peace Canyon dams on the Peace River in northern British Columbia. Flow fluctuations (natural or regulated) can disrupt the ice cover in the early stages of ice cover formation leading to the potential for freeze-up ice jam flooding at the Town of Peace River, AB and other locations. Observations of stage data on the Peace River in British Columbia and Alberta indicate that anchor ice formation and release can create relatively large stage fluctuations, or Anchor Ice Waves (AI waves). This study examines Shallow Water Ice Profiling Sonar (SWIPS) and Acoustic Doppler Current Profiler (ADCP) data, collected during an AI wave that occurred in November 2014, to gain insight into how large expanses of anchor ice can influence the hydraulics of the river. Total water and ice discharge, and ice floe properties, were computed based on data from the two sensors. This allowed differentiation between a frazil ice floe dominated ice run and an anchor ice floe dominated run so that the volume of anchor ice in the AI wave could be calculated. The computed discharge from the ADCP was compared to river ice modelled discharge and the open water rating curve to help identify opportunities for future studies that could inform development of the model to include the effects of AI waves on discharge and ice volume calculations. The computation of discharge was also performed to identify the magnitude of AI waves that have the potential to destabilize the formation of the downstream ice cover, which can lead to freeze-up ice jam formation and flooding. SWIPS data not only identified periods of complete anchor ice release as a result of warm water arriving from upstream but also partial releases during maximum supercooling and frazil production. Another portion of this study focused on field measurements of anchor ice porosity during the2015-2016 winter in order to establish the correct value to be used in this and subsequent studies and for model input.


Year: 2016

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