Extreme cold and temperature swings in Alberta this week have created a somewhat unusual formation along Calgary’s Bow River.
On Thursday evening, Alberta Environment and Protected Areas issued an “ice advisory” after melting and moving river ice forced flooding near the Calgary Zoo and Inglewood.
“That new ice cover that formed in the cold weather became unstable and collapsed forming what we call a freeze-up ice jam,” said Stefan Emmer, a river hydraulics and ice engineer with Alberta Environment and Protected Areas.
The “freeze-up jam” between Harvey Passage and the 12 Street Bridge was pushing water levels to rise by about two metres on Friday, closing some pathways.
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And while the immediate concern about flooding continues to melt away with a warming trend, the province and city will need to carefully monitor the jam throughout the season.
“It’s uncommon for it to happen exactly in that location,” said Emmer. “We haven’t seen an ice jam like that in the past number of years.”
Alberta has seen very real impacts from ice jams before, including in April 2020, when a 13 kilometre ice jam on the Athabasca River forced thousands out of their homes in Fort McMurray.
It’s something Calgary also has experienced before.
In 1950, overnight flooding forced thousands on the Bow River between Centre Street and 4 Street S.W. to flee their homes. Sudden icy, wet evacuations in -20 Celcius temperatures sent several people, including emergency responders, to hospital.
A provincial commission was formed in 1952 to investigate the cause and possible mitigation.
The report recommended the construction of the Bearspaw Dam, which was completed two years later.
“Freeze up ice jams like this did become less common after the construction of that second dam,” said Emmer. “It moves this warmer water temperature downstream.”
More extreme temperatures are required to create the kind of freezing and thawing that created this week’s ice jam. And greater, more frequent temperature swings — which have been linked to climate change — could continue to create a chilling trend.
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