Understanding the City’s Stormwater System

How Does the Stormwater System Work?

The stormwater system is designed to drain rainwater in order to reduce water accumulation on streets and around buildings. In Pointe-Claire, this system is separate from the sanitary sewer system. This means that rainwater and wastewater flow through different pipes, which helps reduce the risk of overloading wastewater treatment plants and limits overflows into the environment.

Unlike the sanitary sewer system, the stormwater system does not treat wastewater. It only collects rainwater runoff from impermeable surfaces such as roads and parking lots.

When rain falls, water naturally flows toward low points, where it is collected by catch basins and directed into a network of underground pipes. Depending on the location, it may also pass through vegetated areas or retention basins before being discharged into a body of water, such as Lake Saint-Louis.

However, like stormwater systems in municipalities across Québec, Pointe-Claire’s system was designed to manage a certain volume of water. During intense rainfall events, it can temporarily reach its limits, even when it is well maintained.

The Infrastructure That Makes Up the System

The Stormwater System

Pointe-Claire’s stormwater system relies on a range of complementary infrastructure that works together to collect, slow, retain, filter and convey rainwater.

Each type of infrastructure plays a specific role in stormwater management. Together, they help reduce water accumulation, ease pressure on the system during heavy rainfall and improve the City’s resilience to extreme weather events.

Conventional Stormwater Infrastructure: Retention Basins and Pipes

Ces installations souterraines ou à ciel ouvert permettent de retenir temporairement l’eau de pluie, pour réduire la pression sur le réseau et diminuer les risques de débordements. L’eau s’y accumule lorsque le réseau est plein, puis est relâchée progressivement lorsque la capacité du réseau le permet.

Green Stormwater Infrastructure

These features naturally absorb, retain and filter rainwater, helping it infiltrate into the groundwater. This reduces runoff and the load on sewer systems, restores the water cycle and enhances the urban environment.

Sponge Parks

A sponge park is a space built at a low point in a neighbourhood to redirect water during intense rainfall. Runoff is diverted toward the basin before reaching the municipal system, which slows the flow and helps prevent the system from becoming overloaded. The park remains dry 95 to 99% of the time. It only fills temporarily during heavy rainfall, then drains in a controlled manner, either through infiltration or toward the sewer system.

Bioretention Cells and Basins

These are slightly depressed landscaped areas made up of plants and filtering layers (soil mix, sand and stone) toward which runoff is directed. They retain water, filter it and allow it to slowly infiltrate into the ground. Smaller cells are often installed as networks in streets and parking lots, while larger basins are located in green spaces, where they can also create habitat for wildlife.

Vegetated Swales

These are shallow ditches built at surface level along a street or path. They collect runoff and guide it in a controlled manner. Their vegetated surface promotes infiltration, filters sediment, slows the flow toward the system and reduces erosion.

Stormwater Curb Extensions

These are vegetated curb extensions with an opening in the curb that allows water from the street to enter. The water is directed toward the plantings, where it infiltrates into the soil rather than flowing directly into a catch basin. Their design, including their shape and concrete curb, also helps slow traffic and make pedestrian crossings safer.

Integration Into Urban Planning

Stormwater management is integrated from the design stage of streets, parks and new residential projects. This helps better distribute water volumes, preserve natural environments and adapt to new climate realities.

Regular Maintenance and Monitoring

The proper functioning of the stormwater system depends largely on rigorous and ongoing maintenance. In Pointe-Claire, municipal crews work throughout the year to inspect, clean and repair the system’s various components.

Preventive Maintenance

Throughout the year, the City carries out:

• Cleaning of catch basins, grates and pipes to prevent blockages.
• Inspection of underground infrastructure using cameras or specialized equipment.
• Targeted repairs on damaged or aging sections.

These interventions help reduce the risk of backups or water accumulation during heavy rainfall and ensure the proper functioning of the system while extending the service life of the infrastructure.

Monitoring During Weather Events

During periods of heavy rain, municipal departments actively monitor the system:

• Monitoring geographically sensitive areas.
• Responding quickly in the event of a blockage.

This work is often invisible on a daily basis, but it is essential to keeping residents safe and limiting the impacts of extreme weather events.

Stormwater Management Plan

In response to the increase in intense rainfall events and evolving urban planning needs, the City of Pointe-Claire has been working since April 2024 to update its long-term management plan to better guide and adapt its stormwater infrastructure.

This plan aims to:

• Understand the current capacity of the system and identify more vulnerable areas.
• Prioritize investments based on risk and climate change.
• Integrate best practices in sustainable stormwater management.

A study in partnership with ÉTS

To support this work, the City has been collaborating since 2025 with a research team from the École de technologie supérieure (ÉTS). This study will help to:

• Model water flows across the City under different rainfall scenarios.
• Assess pressure points in the existing system.
• Propose solutions adapted to the short, medium and long term.

The results of this study, expected during 2026, will guide future planning decisions, taking current and future climate realities into account.

Debunking Common Misconceptions

1. If streets are filling with water, it is because the sewer pipes are too small. We just need to make them bigger.

It is not that simple.

The stormwater system was designed according to realistic standards based on the typical rainfall at the time it was built. During intense or exceptional rainfall events, the volume of water can exceed this capacity, as it does in all cities. Enlarging pipes can sometimes help, but it requires major and costly work and does not solve every issue. A combined approach that includes natural solutions and changes in habits is often more effective and sustainable.

2. Trees and greenery do not make a difference.

On the contrary.

Trees, plants, permeable soils and green infrastructure, such as rain gardens and vegetated swales, help slow and absorb water. Tree leaves temporarily retain some of the rain, which then reaches the ground more slowly. This reduces the rate of runoff and eases pressure on the system. It is a natural and effective solution that complements underground pipes.

3. If there is too much rainwater, it is because of new condos.

New buildings are not the direct cause.

They must comply with strict stormwater management regulations, including retention systems on their property. The challenge is more related to the intensification of rainfall, the aging of the system in certain areas and the fact that older developments were not designed for these conditions.

4. We had a year since the Debby storm to fix this.

Stormwater management takes time.

Analyzing the impacts of an event, planning solutions, securing budgets, designing the work and carrying it out cannot be done in just a few months. The City is taking action, but some projects require several steps and take place over a number of years.

5. It was an exceptional event.

Yes, and these events are becoming more frequent.

Even though intense rainfall may seem rare, this type of event is happening more and more often because of climate change. The system therefore needs to adapt to this new reality, as do residents.

6. We just need to improve the sewers.

This is already underway, but it is only part of the solution.

The City maintains and modernizes certain sections of the system, but it is also focusing on prevention, urban planning and resident collaboration to build overall resilience.

7. This is only the City’s problem.

The City has an important role to play, but it cannot do everything alone.

Every resident can take concrete steps to protect their property: maintaining gutters, installing and maintaining a backwater valve, directing water away from the foundation, building a rain garden and more. Flood resilience is a collective effort.

How to Stay Informed?

The City of Pointe-Claire offers several ways to stay informed about stormwater management, ongoing projects and the progress of measures being implemented.

• Our website: this page is updated with the latest information about the stormwater system. To learn more about steps you can take at home, visit our Emergency Measures page.
• Newsletter and municipal bulletin: receive important news and the latest updates on work and stormwater-related initiatives directly.
• Social media: follow the City to stay informed, discover useful facts and learn more about the stormwater system.