Intensity, location of rain will determine if region gets hit with more flooding
With a wet forecast ahead, the risk of more flooding will depend on how intense the rain will be and where it will fall.
That will determine if those living in flood-prone areas will get a respite, or will have to leave their homes in a boat.
“Right now, it is stabilizing, but we’ll have to wait to see if the levels go down before the rain starts again,” said Chloé Alassimone, a hydrologist at Hydro Météo, which analyzes flood risks in the province.
Alassimone said the Ottawa River, Mille-Îles River and the Rivière des Prairies reached their peaks Tuesday night into Wednesday, and seemed to be stabilizing on Thursday. She said they could rise again in the coming days, but because it’s hard to predict how much it will rain, and how much the levels will decrease before the rain, it’s difficult to say if there will be more flooding.
With one of the wettest months of April on record, it wasn’t the amount of rain that fell that caused problems, but the intensity of it, Alassimone said.
Because it fell in great quantities all at once, the water had little chance to flow downstream, ultimately to the ocean.
Snow is also still melting up north, in the Mont Tremblant region and further north, adding to the volume of water.
In Pierrefonds, Senneville, Ste-Anne-de-Bellevue and Île Mercier, where about 100 households were affected by flooding Wednesday, it took two days after a heavy rainfall for the water to rise on their side of the river. So even if there appears to be no flooding after a period of rain, it could take a few days for the full effect to be felt, Alassimone added.
“This is a very exceptional flooding season,” she said. “We haven’t seen levels like this in 40 years.”
She added that it could take several days or even weeks of dryer weather for the levels to recede.
Many residents in Pierrefonds and Île-Bizard said they would have liked Hydro-Québec to hold back some of the flow from the hydroelectric dam at Carillon, near the Ontario border.
However, that dam doesn’t control the flow of water, said Serge Abergel, a spokesperson for the provincial corporation.
He added that the Carillon dam only holds about 30 per cent of the water that flows into the Ottawa River, but Hydro-Québec is holding back some of the water at the Mercier Dam up north in Grad-Remous, Quebec, north of Mont-Laurier.
“We’re looking at the water levels right now, and we’re releasing the amount of water so as not to cause problems down the road,” Abergel said.
As for the south side of the West Island, so far no flooding has been reported. The level of Lac St-Louis is influenced by the Ottawa River and the Great Lakes. The International Joint Commission, a U.S. and Canada body that manages the waterway, said in a statement it will maintain the level at Lac StLouis for the “foreseeable future.”
“Coastal jurisdictions should prepare for the possibility of major coastal flooding as storms frequently occur at this time of year,” the commission said. “These high water levels are a result of exceptionally wet conditions and high water supplies, and would have occurred under any regulation plan.”