In Canada, tar is replaced by plants

Published on 03/10/2022 | La rédaction


Say goodbye to tar in the city. How do you do it? By removing it! The idea behind this Canadian project: remove the asphalt to reduce urban heat and allow the soil to better absorb rainwater.

"Now, when we do job interviews, it's on the grass that it happens," says Audrée Boudreau, who puts herself close to the green when she recruits. Previously, instead of this little green pathway next to her association's offices in Salaberry-de-Valleyfield, near Montreal, there was tarmac. " It used to be the parking lot here, so it's quite a change!" Now, native plants have taken over the area. "It's growing fast. We have bees, quite a few insects... it's a little jungle."

To transform this 300m2 tarred place into a plant island, Audrée and nearly eighty other volunteers depaved. The town hall, a partner in the local project supported by the Montérégie regional environmental council, came to break up the pavement, and then the participants removed the blocks of tar with their arms. " We had the most fun part, finally!" says the neighborhood life agent. Next, soil was dumped and volunteers planted. "It was a heat island and now there are plants, trees. You can feel the coolness when you walk by."

Better regulating rainwater

Under the Pavement is the brainchild of the Montreal Urban Ecology Centre (Ceum), a non-profit organization that seeks to transform public space "by and for citizens. It has been carrying this project of demineralization of urban space since 2017, the date of the first depaving, in Montreal. Since then, they have launched about fifteen. In the cities that wish to do so, Under the Pavement attacks parking lots that are too big or schoolyards that are covered in concrete, to "free themselves from the waste of the city.The idea is to get rid of the asphalt," explains Véronique Fournier, the project's executive director. "The idea is to make the city more ecological, to transform the living environment. We start from the fact that in our cities, everything has been built by mineralizing and all the green spaces have already been planted. So we have to gain meters on the concrete.

This has several advantages, including improving the absorption of rain by the soil. In the city, nearly 60 percent of rainwater runs off into the sewers, which can quickly become saturated during intense rainfall. "Putting greenery back in will ensure that the soil is more permeable. With climate change, rainfall is falling faster and harder, so clearing is a tool to fight [flooding]," says the Ceum director.

Since the beginning of Under the Pavement, she calculates that she has removed more than 2,500m2 of asphalt. Each year, 700 kilograms of pollutants have been diverted from the waterways, and 2,700m3 of water have ended up in the ground and not in the watercourse.of water ended up in the soil and not in the sewer system thanks to demineralization, according to Ceum.

By replacing asphalt with plants, depaving also helps combat the heat island phenomenon. In the city, the temperature can rise up to 12°C above a nearby rural area. This phenomenon has multiple causes: the loss of forest cover in urban areas, the impermeability of materials, their thermal properties, greenhouse gases and anthropogenic heat.

"We have the feeling of changing things when we say bye-bye to asphalt".

These initiatives are becoming increasingly popular in Quebec and elsewhere, according to Alain Paquette, a professor of biological sciences at the Université du Québec à Montréal, who is exploring urban demineralization. He is currently interested in "draining ledges," vegetated sidewalk extensions that absorb runoff. According to him, the effect of demineralization, on small surfaces, is minimal. "But if you demineralize a lot, over large areas, then yes, you start to have interesting flows to limit flooding."

Beware, however, of the potential unintended effects of these initiatives: "In a city like Montreal, we have a challenge. The water that runs off the streets carries pollutants, especially in winter with the de-icing salts," he says. These contaminants could end up in the newly released soil and then in the water table.

So, before clearing the ground, the project must be well defined with the neighbors. Even though Véronique Fournier assures us that she receives few negative reactions, "there can be questions. Some people wonder if we are taking away too many parking spaces. It's important to make everyone aware of this. Audrée Boudreau, for her part, remembers that some local residents had gritted their teeth at the beginning of the project. "We had complaints from citizens about the choice of plants planted. Grasses were flying into their homes, so they had to sweep their stoops. Nothing major. Someone also drove into our flower beds: a tree was pulled out."

Once de-paved, the area should not be forgotten by the volunteers who created it with their hands. "We put in a lot of native plants. The idea is to let them grow naturally, without them being invasive. We're trying to find a balance, it's not easy," says Audrée Boudreau with a laugh. Another challenge: "Providing maintenance. Is it the role of the volunteers? Is it the town hall's role? You have to know that from the start of the project, otherwise you're a bit lost," says Boudreau, who has since completed another depaving project in her city.

Over the 2021-2023 period, Sous les pavés plans to demineralize eighteen sites in nine regions of Quebec. Three pilot cities will also integrate the project into their communities. Beyond the tar removed, the degrees less and the greenery more, Audrée Boudreau explains that these de-paving experiences have created lasting bonds in the community. "Everyone has something to do, whether you are an adult or a child. We feel strong, useful! We feel like we are making a difference when we say bye-bye to asphalt."


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