Infrastructures and developments designed to capture and absorb heavy rainfall

Last updated March 12, 2025
Reading time: 2 min

The increasing number of episodes of very intense rainfall due to climate change are causing significant damage. With a view to becoming more adaptable, Montréal is maintaining and updating its infrastructures, building water retention structures and developing absorbent natural spaces.

Manage underground infrastructure

The city’s underground system is maintained regularly and systematically. Maintenance work helps us understand the system, particularly the sumps and pipes (from the street to the wastewater treatment plant), and take preventative action as needed. In addition, whenever construction or repair work is performed, underground systems are also upgraded and if necessary, repair or reconstruction work on pipes is carried out. 

Building huge ponds to capture and retain water 

Montréal also has retention structures across the island where hundreds of thousands of cubic metres of water can be collected. These basins limit direct overflows in natural waterways and help reduce the risks of urban flooding and backflow.

These retention structures can be: 

  • A body of water
  • A basin or lake on the surface
  • An underground retention basin made of reinforced concrete, with or without a pumping station
  • Oversized sewer mains 

These infrastructures are costly for the community and building them is complex. It can take years, if not more than a decade, for them to be ready for service. 

Redirecting water from the streets to absorbent spaces 

Sponge parks 

The characteristics of a resilient park are very similar to those of any other park except that the resilient park is designed as a depression. This means that the park is built at a lower level than the adjacent streets. During severe thunderstorms and torrential rains, water from nearby streets can be redirected to the park (by the principle of gravity) to relieve the sewer system. 

The slopes of these parks are generally gentle and easy to cross on foot. Water accumulates gradually in the park only during heavy rains. After a rain, when the sewer system discharges, regulators release water into the system, and the park becomes functional again. 

Resilient parks are like multifunctional spaces. They can offer all the same activities found in an urban park. However, its plants and street furniture are specially adapted to be immersed in water at times. 

The principle of the resilient park is based on the idea of choosing to flood a specific space to prevent water from accumulating on the street and flooding buildings.

Rain gardens 

These are green spaces that collect rainwater to let it infiltrate the ground directly. 

When repairing streets, curb extensions, tree pits and flowerbeds are converted by being developed below street level. Openings are created on sidewalk curbs so that water can flow in from the sidewalk. 

Green infrastructures make it possible to collect light rain and reduce the number of overflows from sewers to waterways, at a lower cost to the community. In addition, they make use of the water to nourish plants while returning it to the ground. 

The great advantage of this approach is that it adds a new function to existing or planned infrastructures and has many additional benefits economically, socially and ecologically.

Multiple benefits for the entire population 

  • Reduced risk of flooding due to heavy rainfall (thanks to rain retention and infiltration functions)
  • Creation of multifunctional spaces that serve as parks most of the time and are retention basins in times of heavy rains.
  • Educational and artistic opportunities for the park, which showcases water (formerly hidden in underground pipes).
  • Cost-effective retention project: Underground retention is more expensive.
  • Reduced heat islands and increased biodiversity. 

These are examples of the measures put forward in Montréal’s action plan to protect neighbourhoods from flooding and provide technical and financial assistance to Montrealers who need to adapt their buildings.