Development of resilient drainage facilities to cope with heavy rain
Montréal is facing climate change phenomena that include episodes of torrential rainfall. Projections clearly indicate that the frequency of these episodes will increase in the years to come. The city is turning to innovative solutions of which Montréal is a pioneer.
Storm water management
Storm water management requires a comprehensive system of infrastructures and a list of processes. Traditionally, maintenance work is carried out regularly and systematically on the city’s underground network. 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.
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. However, 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.
In recent years, like everywhere else in the world, Montréal has had to contend with flooding caused by heavy rains and climate change. These heavy rains discharge massive amounts of water over a small area for a short period of time. No system has the capacity to handle this immense amount of rain. The sewer system simply cannot route all rainwater underground. It is for this reason that the Montréal now uses rainwater management infrastructures above ground that work in conjunction with the underground sewer system.
Adapting and redirecting storm water
Adapting means accepting that storm water will accumulate on roadways and in public spaces during heavy rains, while controlling the spaces where water will accumulate. Measures can be taken to direct this water to specific areas, allowing for better management of these extreme situations. Developing green infrastructures, also known as resilient or sponge infrastructures, is one such measure.
Storm water management must be an integral part of urban planning. In this regard, Montréal is focusing on actions that involve:
- Installing green infrastructures to infiltrate water into the ground when repairing public property like curb extensions, tree pits and bioswales.
- Creating resilient public spaces to receive and temporarily retain water, such as parks and public squares or recreational areas towards which street runoff is also directed.
Green drainage infrastructures
A green drainage infrastructure is like a rain garden. It consists of a green space at a lower level than the adjacent ground. It is developed to collect rainwater that can 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. Residents can do the same by diverting their gutters to channel water to their lawns and plants rather than waterproof surfaces.
Development of resilient parks: Multifunctional spaces
Resilient parks, also known as sponge parks, receive rainwater and retain it temporarily to reduce the risk of water accumulation on the streets during heavy rains.
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.
After a rain, when the sewer system discharges, regulators release water into the system, and the park becomes functional again. 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. Areas are chosen to flood voluntarily, instead of areas randomly being overtaken by floodwater.
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 use of space, which is limited in urban areas, is not compromised.
Resilient parks are an environmental, sustainable and tangible initiative. Unlike underground developments, these surface developments are an efficient and more economical way to reduce the impacts of heavy rains. 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. In particular, resilient parks help reduce heat islands and increase biodiversity.
Resilient parks are also safe. The slopes of these parks are generally gentle and easy to cross on foot. Water accumulates gradually in the park only during heavy rains. The water that accumulates empties in the hours following the storm (within a maximum of 24 hours).
Multiple benefits for the entire population
- Reduced risk of flooding due to heavy rainfall (thanks to rain retention and infiltration functions)
- Multifunctional space, since the area is developed as a park for public use 99% of the time (and serves as a retention basin 1% of the time.) In a dense urban context where land is expensive, this is a responsible and efficient use of space.
- Educational and artistic opportunities for the park, which showcases water (formerly hidden in underground pipes).
- Cost-effective retention project: Underground retention is more expensive.
- Enhancement of the urban environment and biodiversity through the creation of more ecological and natural planting areas.
Adoption of legislative frameworks from a resilience perspective
Legislation must also be consistent with the city’s new realities and actions. Updating urban planning and construction by-laws is part of the actions the city is taking to support these initiatives and ensure coordinated work among its residents. Owners of both new and existing buildings will be able to adapt their homes to these new realities.
A collective action plan
With Montréal’s development strategy, which places climate change at the heart of urban development policies and projects in order to reduce its impacts, the city has become one of the most innovative municipalities in terms of integrated and sustainable stormwater management.
The implementation strategy for green and resilient development is one of the three main components of the action plan for flood resilience during heavy rains set out by the city. It is the result of a comprehensive and coordinated vision and approach that engages the entire community in a process of adaptation.
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