This text is taken from the Courrier de la Planète of November 8, 2022. To subscribe, click here.
The rain better watch out! Place des Fleurs-de-Macadam, on Le Plateau-Mont-Royal, was sprayed last summer with two particularly heavy downpours, one in June, the other in September. It has now undergone a controlled flood test which is giving city officials valuable details about its potential to absorb downpours.
Thursday, November 3, 2 p.m. Fire hoses spit water into the public square. Blue-collar workers simulate a 50 mm rain that falls in three hours. Strollers are lounging on the park benches, while the puddle of water is a stain at their feet. The liquid flows to the sides, where it fills a slight depression in the ground. As the water rises, the wood chips lift and dance.
“We measure the water level, both in the public square and in the surrounding rain garden. Then, we’ll see how long it takes before the water is completely absorbed,” explains Marie Dugué, head of the green infrastructure team at the City of Montreal’s Water Service, on the edge of the pond. temporary.
Flowmeters record the volume of water injected into the floodplain. Up to 120 cubic meters of water can normally fit in this natural reservoir made up of stones, plants and trees. After a heavy downpour, the water seeps into the ground and quietly moves towards the water table. In other words, this “rain garden” reduces the volume of water that ends up in the sewer. In doing so, it protects the surrounding infrastructure from unexpected flooding.
On this beautiful autumn day, part of the water invading the public square comes from a pipe placed on Mentana Street. Due to the local topography, the liquid flows towards the floodplain. Drops in the concrete curb allow water to enter the site. These developments are not very sophisticated, but will be of great importance in adapting the city to climate change.
“Before, the dominant paradigm was always to evacuate the water as quickly as possible, so that we wouldn’t see it,” underlines Rémi Haf, a planning consultant at the Water Department of the City of Montreal. Now, landscape architects are incorporating the water cycle into their designs. They can “unleash their madness,” says Haf, who played a crucial role in bringing rain gardens to the metropolis.
Moreover, building a flood-prone square does not cost more than building a traditional public square, he says. “There is often less engineering work underground when you make a rain garden. » No need for sumps that evacuate the water to the sewers. In addition, resilient parks reduce the need to construct underground rainwater retention reservoirs, which are very expensive to construct.
In addition to Place Fleurs-de-Macadam — named in honor of the author of the song of the same name, Jean-Pierre Ferland, whose father ran a garage there in the last century — the City of Montreal has three other “resilient parks” that soak up rainwater.
Several other projects are underway, including the Irma-LeVasseur park in Outremont, which will be able to store 3,000 cubic meters on the surface, the equivalent of an Olympic swimming pool. In all, 9000 cubic meters will be added to the municipal capacity by April 2025.
In the short term, the City creates flood-prone areas by “opportunism”, according to the park projects of the boroughs, explains Ms. Dugué. “In the medium term, we are looking at the master plan for green spaces in the boroughs, to help them prioritize which parks to do first based on flooding issues,” she continues. Adaptation to climate change will therefore become the norm, not the exception.