Proactive bylaw amendments

In accordance with Ville de Montréal’s Urban planning and mobility plan, Saint-Laurent has recently introduced bylaw amendments to help property owners better protect themselves against urban flooding during heavy rainfalls. The new provisions apply to the entire territory and mainly concern the design of parking areas and the conditions for authorizing basement dwellings.

Back in the 1980s, Saint-Laurent adopted bylaw 1047 concerning the retention of rainwater on private properties. This bylaw was subsequently incorporated into Ville de Montréal bylaw 20-030, which more extensively regulates connections to water and sewer systems as well as stormwater management at the municipal level.

In 2023, Saint-Laurent updated its bylaw on sustainable parking, dating from 2009 and already improved in 2015. This made it possible to raise the requirements for greening, water management and biodiversity protection in the development of parking areas for industrial, commercial and service uses as well as for residential areas. In 2023, Ville de Montréal also published a map of basins identifying areas where water is likely to accumulate during intense downpours.

In 2021, Saint-Laurent adopted a Climate emergency plan to mobilize the entire community around mitigating climate change and adapting to its impacts.

8 open-air retention basins

Since the mid-1990s, seven open-air retention basins have been built. Each basin can hold around 10,000 m³ of water—the equivalent of 3 to 4 Olympic-size swimming pools. 

Two of these basins were built in the 1990s and the next five after 2000. All are located in the Nouveau Saint-Laurent and Bois-Franc areas: 

• Bassin Dr. Bernard-Paquet (1994)
• Bassin de la Brunante (1995, Parc Marcel-Laurin)
• Bois-Franc: Bassin du Suët (lac E), Bassin du Suroît (lac D) and Bassin du Noroît (lac A)
• Nouveau Saint-Laurent: Bassin Henri-Thomas-Scott and the basin in Parc Philippe-Laheurte 

An eighth basin is planned for Nouveau Saint-Laurent in Parc Arthur-Lessard.

15 medium-sized retention basins

Some 15 medium-sized basins have also been integrated into residential development. Some are “dry basins” and act as sponge areas. 

In particular, they can be found in the following locations:

• Parc Aimé-Caron,
• Parc Raymond-Vidal
• Placette Thérèse-Cadorette,
• Along rue Guénette (2) and boulevard Cavendish (2 facing Place Édouard Dufresne)
• 2 basins in Parc Phillippe-Laheurte
• Parc Urgel-Archambault
• Parc Hartenstein
• Parc Guillaume Bruneau
• Square du Solstice (Bois-Franc)
• Square Boréal (Bois-Franc)
• Square du Petit Prince (Bois-Franc)
• Spaces along boulevard Poirier (Bois-Franc)

12 underground retention basins

Since the 1980s, a dozen underground retention basins have been built in streets and parks to relieve the existing network, including at the following locations: 

• Rue Saint-Aubin
• Rue Tait
• Rue Marcel
• War-Time sector
• Technoparc sector
• Parc Saint-Laurent
• Parc Cousineau (south side and dog park)
• Parc Harris
• Boulevard de la Côte-Vertu (between rue Saint-Germain and avenue O’Brien)
• Ouimet parking lot
• Rue Crevier and rue Gohier (south ends)

To minimize sewer backups, the size of the pipes on these streets was also increased during roadwork.

Green spaces and natural solutions

Over the past fifteen years, several green spaces have also been landscaped as bioretention areas (also known as rain gardens), notably at the following locations:

• Rue de la Sorbonne
• Rue Crevier (between rue de l’Église and rue du Collège)
• Rue Claude-Henri-Grignon (two drainage ditches)
• Rue des Outardes (south of Bassin Henri-Thomas-Scott)
• Parc Aimé-Caron (area to be redeveloped, work scheduled for 2026)
• Parc Marcel-Laurin woodland (work scheduled for 2026-2027, over a period of two years)
• Future Parc Noëlla-Douglas (in the Cité Midtown residential development, work scheduled for 2026-2027)

These street-side green spaces are designed to intercept runoff, irrigate greenery and allow infiltration into the soil.

Over the past five years, sustained efforts have been made to increase green spaces. For example, thousands of trees—around a thousand a year for the past 10 years—have been planted every year to help water infiltration. 

More recently, rain gardens have been developed at Square Rambler and Square Norseman to mitigate the risks of flooding and backflow.

Sponge parks are also in place or under development at the following locations: 

The characteristics of a sponge park are very similar to those of any other park, but it is developed at a lower level than the adjacent streets. During a violent storm or heavy rainfall, water from the surrounding streets can be redirected there (by the principle of gravity) to relieve sewer systems.

Although this project is still under study, some public parking lots could be transformed into “sponges” to better manage stormwater. This is particularly the case for the Centre des loisirs parking lot, which should become green and eco-responsible by 2026. The Ouimet parking lot (between rue de l’Église and rue du Collège), the green space in front of the Bibliothèque du Boisé and its green roofs as well as those of the Ateliers municipaux and the Parc Painter chalet are also innovative green installations designed with this in mind.