Floods in Montreal will happen again. Maybe soon. What can we do about it?

CBC

16-07-2025

Eva Szymkowiak was among the Montrealers starting the week dealing with the aftermath of a storm that dumped more than 70 millimetres of rain over the city in just a few hours.
For the second time in just under a year, the longtime resident of Montreal's Saint-Laurent borough, says her building's parking garage on Thimens Street was completely flooded.
Last year, she says both their vehicles were ruined in a flood. But on Sunday, Szymkowiak says they saw the water accumulating from the storm and she luckily had time to move her car and warn others in the building.
One neighbour described seeing the manhole covers on the street being blown off and the water making its way into the building through the indoor garage. "Somehow this street doesn't absorb [...] huge amounts of water," Szymkowiak said.
Szymkowiak and her neighbour are hoping the city steps up to fix the problem. Faced with repeated flooding across multiple boroughs, officials are attempting to find long-term solutions — some even introducing bylaws designed to mitigate flood risk and exposure.
'Every neighbourhood, every street is different,' says mayor
Montreal Mayor Valérie Plante visited those impacted by flooding in the city's Ahuntsic-Cartierville borough on Monday.
"There isn't a unique solution for the entire territory," she said. "Every neighbourhood, every street is different."
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She pointed to various initiatives being carried out by the city to reduce the impact of flooding, including overhauling the sewer infrastructure in high-priority areas and building green infrastructure, such as sponge parks and retention basins.
Maja Vodanovic, the executive committee member responsible for water, said several criteria help determine which areas are high priority, including the number of people affected in an area, whether it's in a low-lying area or prone to flooding.
Overhauling sewage network not the solution, says expert
Jean-Luc Martel, a professor in the construction and engineering department at the École de technologie supérieur in Montreal, said there is often a lot of emphasis placed on the need to redo the sewer network.
But retrofitting the sewage network as a whole would be expensive, he says. In some cases, putting in bigger pipes would just displace the problem by moving the water downstream.
"It's not a question of the size and the capacity of the sewer network. They're not designed to deal with those events," said Martel. "That's not [its] job."
To mitigate flooding, boroughs have to look at what's happening at the surface, says Martel, and reduce the amount of runoff making its way into storm sewers to avoid overwhelming the network.
Green infrastructure can help. He says homeowners can also do their part by having rain gardens and disconnecting gutters to allow the water to be absorbed by the lawn.
Ultimately, though, Martel says the main issue are basements.
"We need to really question ourselves as a society. Do we need basements?" said Martel.
"After the sewer is full, the water stays on the surface and then it goes with gravity. It goes to the lowest point," he said.
Mitigating flood risk and exposure
With the intensity and frequency of extreme rain set to increase, the City of Montreal says it wants to make it easier for homeowners to make changes to create a more resilient home.
That can include using waterproof materials like ceramic tiles in flood-prone basements, or installing watertight garage doors, says Maja Vodanovic, the executive committee member.
"We want to make it more simpler for those kind of projects to go through. We are working on changing our regulations to streamline those projects," Vodanovic said.
Regardless of the neighbourhood, or borough, the city of Montreal said its RénoPlex program, for buildings with one to five dwellings, provides financial assistance to homeowners for renovations or flood protection work on their property.
The borough of Saint-Laurent has taken action and adopted a new bylaw last month which will allow homeowners to level up downward sloping garage entrances.
It also outlines conditions for parking lot layouts and states that new driveways should be designed in a way to prevent rainwater from flowing onto private property.
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After several floods in Quebec, the borough of Saint-Laurent has decided to allow property owners to level up their inclined driveways. It's also put in place a measure that prohibits basements to be used for certain purposes.
But the borough isn't quite ready to remove basements from the equation.
Citing the ongoing housing crisis, it said in a news release, the borough will continue to allow for dwellings in basements, even in new constructions, provided "flooding risks are reduced to a minimum."
Borough Mayor Alan DeSousa, says basement usage for daycare centres and seniors' residences will be limited.
"If kids are in the basement doing activities and water comes very quickly those kids are vulnerable," he said.
Other boroughs have different rules.
Rosemont–La Petite-Patrie, is taking a tougher stance and is not allowing the construction of 100 per cent basement dwellings anywhere on its territory, except through special exemptions for large-scale projects that benefit the community and meet criteria ensuring resiliency.
Homeowners, however, will be allowed, under certain conditions, to expand the living area of their home by developing an underground living space. Basement use will continue to be allowed for things like garbage storage, laundry rooms, and parking areas.