Extreme cold and temperature swings in Alberta this week have created a somewhat unusual formation along Calgary’s Bow River.
Thursday night, Alberta Environment and Protected Areas issued an “ice advisory” after river ice melted and moved, forcing flooding near the Calgary Zoo and Inglewood.
“That new ice cover that formed in the cold weather became unstable and collapsed and formed what we call a freezing ice jam,” said Stefan Emmer, a river hydraulics and ice engineer with Alberta Environment and Protected Areas.
The “freeze jam” between Harvey Passage and the 12 Street Bridge caused water levels to rise by about two meters on Friday, closing some paths.
And while immediate flooding concerns continue to fade with a warming trend, the province and city will need to closely monitor the jam throughout the season.
“It’s unusual for it to happen in that exact spot,” Emmer said. “We have not seen such an ice jam in the last 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 from their homes in Fort McMurray.
Ice jam causing flooding in Fort McMurray shrinks to 13km in size: officials
This is something Calgary has experienced before.
In 1950, overnight flooding forced thousands to flee their homes on the Bow River between Center Street and 4th Street SW. Sudden freezing, wet evacuations in -20 Celsius temperatures sent several people, including emergency personnel, to hospital.
A provincial commission was set up in 1952 to investigate the cause and possible mitigation.
Construction begins on the Springbank downstream reservoir project
The report recommended the construction of the Bearspaw Dam, which was completed two years later.
“Ice freezing like this became less common after the construction of that second dam,” Emmer said. “It moves this warmer water temperature downstream.”
More extreme temperatures are needed to create the kind of freezing and thawing that created this week’s ice jam. And larger, more frequent temperature swings — linked to climate change — may continue to create a cold trend.
© 2022 Global News, a division of Corus Entertainment Inc.