The new mapping carried out by the Metropolitan Community of Montreal (CMM) according to the rules established by Quebec will double the number of residences which are now in flood zones in Montreal and its suburbs, or more than 15,500 buildings.
The proposal arises from the submission by Quebec 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,” recalled Nicolas Milot, director of the Ecological Transition and Innovation Department at the CMM, during a technical briefing on Friday.
The rules also introduce a new zone designation system. Previously, areas were identified based on the recurrence of floods, i.e. 0-20 years (high current) and 20-100 years (low current). From now on, zones will be designated based on very high, high, moderate and low exposure with colors ranging from intense red, for the very high exposure zone, to yellow for the low exposure zone.
Already, last June, when the Minister of the Environment, the Fight against Climate Change, Wildlife and Parks, Benoit Charette, announced the update of the regulation concerning flood zones on the scale of the province, concerns were great. Quebec already estimated that nearly 77,000 homes, or 2% of the population, would be in flood zones, whereas currently there are 22,000.
The preliminary maps developed by the CMM based on the rules imposed by Quebec mean that 15,508 buildings (or 19,000 housing units) are now found in flood zones, including 3,204 in the “very high” exposure zone. “This is not trivial on the scale of Greater Montreal [compte tenu] of the housing crisis”, indicates Nicolas Milot, emphasizing that there are major constraints to moving these residences whose land value globally reaches $9.9 billion.
By examining a sample of sectors, the CMM comes to the conclusion that the number of buildings found in flood zones has doubled in the region.
The case of Sainte-Marthe-sur-le-Lac
This system therefore ensures that, for example, a large part of the municipality of Sainte-Marthe-sur-le-Lac finds itself in a flood zone whereas previously, only a few houses were part of it. As it has a dike, the city is however found in the yellow zone on the map (low exposure zone). Without a dike, it would be in the red zone with a precautionary zone of 10 meters. “It’s a big concern,” recognizes Nicolas Milot. “Historically, Pointe-Calumet and Sainte-Marthe-sur-le-Lac were not in flood zones. To see themselves appearing in the yellow and red zones, they [les citoyens] are afraid for the value of their home, their ability to mortgage and be insured. »
Zero risk does not exist. On April 27, 2019, the dike of Sainte-Marthe-sur-le-Lac gave way, forcing the evacuation of 6,000 residents. At the time, however, Nicolas Milot recalls, there were no regulations to govern this type of protective work nor standards to impose regular frequency inspections. With its new regulation, Quebec addresses these shortcomings and significantly reduces the risks, he says.
In this context, the CMM considers that sectors containing protective infrastructure, such as a dike, should be identified according to distinct 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 found in several municipalities such as Sainte-Marthe, Deux-Montagnes, Rosemère and Bois-des-Filion, believes the CMM. “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. » He cites the case of Pierrefonds, which diversion canals or sponge parks alone cannot protect.
Under Quebec’s new regulations, new maps must also take into account the uncertainty linked to climate change by providing a “precautionary margin”, as well as the effect of water management systems, such as water dams. Hydro-Québec or the reservoirs of the Great Lakes. “The floods we are experiencing are the result of management and not of nature which simply sends water into these large systems,” recalls Nicolas Milot.
Financial issues
On Monday, during a meeting of the CMM council, elected officials representing the 82 municipalities in the Montreal region will be asked to vote on the CMM’s mapping proposal, which also submits some recommendations. In addition to the application of separate standards for areas protected by protective structures, the CMM judges that the government should allow the reconstruction of existing buildings into resilient buildings in sectors of moderate to high exposure based on risk, rather than to “freeze” the territory with bungalows for example or to leave owners with buildings which risk losing a lot of value without any improvement being possible. “Currently, as written, the regulations prevent it,” underlines Nicolas Milot.
Added to this is the fact that Quebec limits aid to disaster victims to $100,000 — which is legitimate, according to the CMM — which will also have the effect of reducing the value of certain houses to zero. “There is not a mortgage lender who will agree to lend money for houses that no longer have the capacity to be rebuilt or to be worth anything in the future. »
According to Nicolas Milot, Quebec estimated that the impact of the new zones would be limited to reducing the value of residences by 4%. The CMM considers that this reduction is “largely underestimated”, because it does not take into account other effects such as access or not to compensation, insurance and above all, access to mortgage loans. And the CMM considers it essential to look into a relocation plan for the areas most at risk.
Citizens can consult the new map online with their civic address. Nicolas Milot warns, however, that certain perimeters could change, because the maps are preliminary and Quebec will have to approve the document developed by the CMM.