Torrential rains in Montreal | A “blue-green alley” to the rescue in Pointe-Saint-Charles

Adapting to climate change involves, in particular, nature-based solutions, such as the “blue-green alley”, a pilot project in southwest Montreal that aims to make infrastructure more resilient and reduce the risk of flooding. .

Last week, torrential rains overloaded Montreal’s sewers and put a strain on the city’s infrastructure. The list of damage caused by sudden rains is long and costly.

The underground network was unable to swallow the amount of water poured from the sky. Roads, like boulevard Décarie, have become veritable swimming pools, houses have been flooded, water has also entered the metro and manholes have literally flown away under the pressure of the water.

But in the Pointe-Saint-Charles district, near building 7, which houses a grocery store, a brewery, a small farm and several community projects, the torrential rains last Thursday do not seem to have caused any damage and it may be thanks to the blue-green lane, which has just been developed by community organizations and two urban planning firms.

“The blue-green lane developments have proven their effectiveness,” said the Montreal Urban Ecology Center on social networks, referring to the torrential rains.

“We are going to do a hydrological analysis, but everything seems to be working as planned, the water contained in the bioretention areas has not gone to join the sewer system already saturated with all this rain”, specified Vincent Ouellet-Jobin, environmental project manager at the Montreal Urban Ecology Centre.


The bioretention areas are essentially small gardens, in the alley covered with earth, rather than asphalt, and which absorb rainwater which comes in particular from the roof of building 7, a former Canadian National railway workshop.

“In Montreal, the majority of buildings have a flat roof, with a drain in the center of the building, so the water from the streets and roofs ends up in the storm sewers which are, in two thirds of the cases, mixed with the domestic sewers. “, explained Vincent Ouellet-Jobin.

But in Blue-Green Lane, Building 7’s drains have been disconnected from the city’s aging sewer system, and gutters are being laid so that rainwater goes directly to bioretention areas where trees grow. plants.

“We added a drain in the center (of the bioretention areas) to absorb the overflow to avoid overflows. In the case of century-old rains, the overflow will go to the sewer network. Which wouldn’t have happened last Thursday.

Demineralize the city

This type of nature-based solution makes it possible to adapt to climate change by offering better resilience to flooding, but also by reducing the effects of heat islands.

“It removes water from the storm sewer system, it reduces the pressure on infrastructure, it also creates a living environment and it helps reduce heat islands because there is no asphalt absorbs the sun’s rays,” said Vincent Ouellet-Jobin.

By watering plants with rainwater, we also avoid wasting drinking water.


“A single blue-green alley won’t make a difference on the island of Montreal, but that’s why we have to build others” and “it has to become a new way of managing water of rain across the city,” pleaded the environmental project manager.

“We’ve known for a long time that we’re going to have to do it and that the professionals have been saying so. The idea of ​​using this type of space to manage rainwater is gaining ground,” said Catherine P. Perras, planning and urban planning consultant at Vivre en ville.

“More broadly, it also brings benefits for the health of the population, because greenery helps filter atmospheric pollutants” and “green spaces help reduce stress and anxiety,” added Catherine P. Perras.

She said that adaptation to climate change in cities includes demineralization, which consists of removing mineral surfaces such as asphalt, to make way for plants.

“We will have to remove the asphalt, clear space to capture the water. It is part of the solutions to adapt to two of the main hazards of climate change in large cities: heat waves and floods. »

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