The rules decreed by Quebec for the revision of the mapping of flood zones will have significant impacts in several municipalities in the Montreal region, including Sainte-Marthe-sur-le-Lac.
The new mapping developed by the Montreal Metropolitan Community (CMM) reveals that 15,508 buildings (or 19,000 housing units), almost double the number previously, are now found in flood zones, including 3,204 in “very high” exposure zones. “. “This is not trivial on the scale of Greater Montreal, [compte tenu] of the housing crisis,” says Nicolas Milot, director of the Ecological Transition and Innovation Department at the CMM. He points out that the property value of the affected buildings overall reaches $9.9 billion.
This mapping exercise stems from the submission by Quebec, last June, of the project to modernize the regulatory framework applicable to flood zones. This requires all Quebec cities to update the mapping of flood zones.
In the metropolitan region, some maps dated from the 1970s, while in other sectors, the maps had been redrawn based on data from 2016. “By updating the maps, we must add data from 2017, 2019 and 2023. These were years of very high water levels,” recalls Nicolas Milot. The new rules also change the designation of zones, which are classified into four colors, from red (very high exposure) to yellow (low).
Already last June, when Quebec announced the update of the province-wide regulation, concerns were great. Quebec estimated that nearly 77,000 homes, homes of 2% of the population, would find themselves in flood zones, while currently there are 22,000.
Sainte-Marthe-sur-le-Lac finds itself in a flood zone, compared to only a few houses previously. But due to its new dike, its exposure zone is described as “low”, and therefore appears in yellow on the map. Without a dike, the city would be in the red zone.
Differential treatment requested
The CMM considers that sectors containing protective infrastructure, such as a dike, should be evaluated according to separate standards since the risk is greatly reduced in the presence of such infrastructure. Differentiated treatment could be granted to the 4,651 buildings located behind a protection structure, as there is also in other municipalities, including Rosemère and Bois-des-Filion. “We should not be surprised, in the coming years, to see requests for new works because, in many cases, this is probably the only solution that we can envisage,” indicates Mr. Milot. He cites the case of Pierrefonds, which diversion canals or sponge parks alone cannot protect.
The new maps must also take into account the uncertainty linked to climate change and the effect of water management systems, such as Hydro-Québec dams.
Monday, during a meeting of the CMM council, elected officials representing the 82 municipalities in the Montreal region gave their approval to the memorandum that the CMM will submit to the government as part of its consultations on the project. In addition to applying separate standards to areas protected by structures such as dikes, the CMM will ask the government to allow the reconstruction of existing buildings into resilient buildings in sectors with moderate to high exposure, depending on the risk. , rather than “freezing” the territory with bungalows or leaving owners with buildings that risk losing a lot of value.
“The stakes are really high,” says the mayor of Laval, Stéphane Boyer. We are changing the philosophy on how to manage flood zones. In the past, houses were built in neighborhoods that were prone to flooding. We shouldn’t have done that. Today, how do we support the citizens who live there? »
Quebec estimated that the repercussions of the new zones would be limited to a 4% reduction in the value of residences. The CMM, however, believes that this drop is “largely underestimated”, because it does not take into account other effects, such as compensation, insurance and, above all, access to mortgage loans. And the CMM considers it essential to consider a rehousing plan for residents of the areas most at risk.
Citizens can consult the new mapping online. Nicolas Milot warns, however, that certain perimeters could change, because the maps are preliminary and will have to be approved by Quebec.