Laval flood risk recedes

Unusual weather turned rivers to thick slush

By Robert Frank

Laval emergency preparedness officials are optimistic that river high water levels that had been threatening Île Jésus—particularly along the shore of Rivière des Prairies—will ebb this week.

“Since Sunday, water levels have been receding,” Laval Police Const. Nathalie Lorrain told The Suburban. “They’re going down slowly, but they’re definitely going down. The warm weather has melted all the bad ice that was blocking the current.”

“The ice is thick, unlike in small rivers where ice starts breaking up in the spring,” she added, “so we also do not anticipate any ice movement.”

The rapid alternation between deep freeze and balmy weather during the past couple of weeks had turned the rivers that surround the city into a thick, supercooled slushy mix— known as frazil—rather than just freezing on top. In addition, the temperature flux could have caused bottom freezing, where ice forms at the bottom of the river, rather than on the surface. That can cause water to well up where the channel is shallow.

That sno-cone-like suspension obstructed the channels surrounding the island and caused the rivers’ water level to rise. City firefighters stocked sandbags last week, to protect residents in case any of the rivers overflowed their banks.

Shorelines in Sainte Dorothée, Laval des Rapides and St. François were particularly at risk during the weekend, when rain combined with unusually high, above-zero temperatures melted accumulated snow—the equivalent of a torrential downpour.

“The land surrounding Lévesque Boulevard in Laval des Rapides is particularly low near the river,” Const. Lorrain explained. “In the event of floods, the city would have placed sandbags there to keep the water from flooding the thoroughfare.”

“The situation could be compounded by bottom freezing,” she added, “where ice forms at the bottom of the river, rather than on the surface, causing the water to well up where the channel is shallow.”

The city used an amphibious boat to break up the slushy, blockages, and paid Hydro Quebec to use its vessels to keep open the channel from near the Pont Viau bridge to its hydroelectric dam on Rivière des Prairies.

Melting Ottawa River could influence outcome

“Hydro Quebec is not obliged to provide assistance, but it has cooperated splendidly with the city,” Const. Lorrain said. “We anticipate that water levels will continue to go down slowly. That’s good news for citizens who reside along the riverfront. They can sleep in peace now.

City officials are continuing to monitor water levels in the rivers surrounding Laval.

“New water flowing from the Ottawa River, could influence water levels during the coming week,” the city’s public safety department said in an internet statement, Jan. 12. “Emergency response crews are on the ground in Sainte Dorothée, Laval des Rapides and St. François to monitor the situation.”

“We will be following river levels closely,” said Const. Lorrain.

Officials urged residents to report signs of flooding: “Water on your property or infiltrating your home or other signs. If in doubt, call the 311 help line.”

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