Clouds to blame for faulty government flood maps, Quebec mayor says

Vaudreuil-Dorion Mayor Guy Pilon blames "amateur" mapmakers for failing to correct flawed satellite images, causing thousands of residents to "panic" at finding their dry homes in newly designated flood zones.

Hundreds of Vaudreuil-Dorion residents 'panic' to find homes in flood zones, despite not having been flooded

A view from a Canadian Forces helicopter shows the flooded region of Rigaud, Que., on April 21, 2019. (Christinne Muschi/Reuters)

To find the problem with the Quebec government's new flood maps, look up.


The government neglected to correct areas on the map obscured by the shadows cast by cloudy skies, according to Vaudreuil-Dorion Mayor Guy Pilon. 

Hundreds of angry residents packed a meeting hall in Vaudreuil-Dorion Thursday evening, demanding government officials explain why their homes were now included in a flood zone, despite being several metres above the high water level. 

"OK, do you want to hear a good one?" Pilon asked CBC Montreal Daybreak host Ainslie MacLellan Friday, before embarking on his explanation.

Pilon said the provincial government was too hasty in creating new zero-to-20-year flood maps.

Municipalities have flood-zone maps already, but many are considered outdated. The government wanted to act quickly to release the new maps, he said, so that after this spring's flooding, building permits would not be issued to homeowners whose properties are inside flood zones. 

The new maps show areas ostensibly at risk of flooding, designated as "special intervention zones," or zones d'intervention spéciales (ZIS), where construction and rebuilding would be put on hold.

Those ZIS include areas that were flooded in 2017 or 2019, as well as those now deemed to be at elevated risk of flooding, based on satellite imagery.

Property owners in those ZIS will no longer be allowed to build or rebuild their homes, and renovations will only be allowed if the total cost of those renovations comes to less than 50 per cent of the property value.

'Really, really amateur'

Vaudreuil Mayor Guy Pilon says the government failed to consult municipalities in redrawing flood zones. (Charles Contant/CBC)

Pilon said there is a reason so many homeowners had been stunned to find their properties listed as within a ZIS, even though they have not been flooded.

The mapmakers "forgot to remove what they call the 'shadow zone,'" Pilon said, referring to clouds. Satellite imagery can be misled by clouds, he explained, and corrections often have to be made by land surveyors, working on the ground, the old-fashioned way.

'Amateur' map-making caused panic, says mayor

Pilon said municipalities could have provided data that would have filled in the blanks. 

"They decided to go with the machine and to work like amateurs — really, really amateur — and to make thousands and thousands of people panic," he said. 

In Vaudreuil-Dorion, Pilon said, about 30 homes were flooded in the 2017 and 2019 floods. But the new zone defined by the government's study included 1,500 homes in his municipality alone. 

The new maps cover 812 municipalities across Quebec and, just like in Vaudreuil-Dorion, hundreds more homeowners in other municipalities, as well, find themselves unexpectedly to be included in flood zones.

Sainte-Marthe-sur-le-Lac, where more than 1,000 homes were flooded in April when the Lake of Two Mountains breached a dike, has been exempted from the limits on repairs because of what Municipal Affairs and Housing Minister Andrée Laforest called the "exceptional" circumstances of that flood.

Laforest says she wants to reassure Quebecers that adjustments will be made to the new maps. 


Verity Stevenson is a reporter with CBC in Montreal. She has previously worked for the Globe and Mail and the Toronto Star in Toronto, and the Telegraph-Journal in Saint John.

With files from CBC Montreal's Daybreak and Valeria Cori-Manocchio