IN SOLUTION MODE – Ditches, retention ponds, reservoirs and landscaping. Quebec City engineers used a range of water control tools to design the Roland Beaudin parking lot, which will open in 2022.
“We control 100% of the water surface that falls on the parking lot,” explains Renée Lanthier, an engineer from Quebec City, during a detailed presentation of the work around the Sainte-Foy market and the new ice cream center. The flow rate introduced into the sewer is controlled there. A fixed flow rate is never exceeded.
Open in full screen mode
A bioretention basin in the Roland Beaudin car park in Sainte-Foy
Photo: Radio-Canada / Claude Bernatchez
Coping with more severe and frequent flooding
The summer of 2023 was marked by exceptional rainfall. On July 10th and 11th, 95 millimeters of rain was recorded at the Laval University weather station. Thirty millimeters on the 13th of the same month and almost 70 millimeters on August 8th. To avoid canal backups and flooding, the city had to release untreated water into waterways like the St. Lawrence River.
Open in full screen mode
Heavy rains in the summer of 2023 forced Quebec City to discharge untreated water into the St. Lawrence River.
Photo: Radio Canada
Municipalities need to manage unified networks in their legacy neighborhoods as they were built in the past. There are two types of networks, explains professor and researcher at INRS Sophie Desmeules. In separate systems, wastewater is sent to sewage treatment plants and rainwater to watercourses. In the oldest districts such as downtown Quebec, Sainte-Foy or Sillery […] Rainwater and wastewater are mixed. […] When there is too much water, there is an overflow of a mixture of sewage and rainwater that enters the waterways.
Municipalities must now develop a range of tools to implement the principle of source code management, as is now practiced in the Sainte-Foy market. Everything is completed up to the sewerage system, explains Renée Lanthier. We have added the concept of resilience; we want to use green infrastructure to try to replicate the natural water cycle a little more. In the event of a significant flood, we can control flow rates before releasing them into the sewer or watercourse.
How it works?
Around the Roland Beaudin parking lot and the roads leading there, trees and plants make this asphalt and concrete area more inviting.
Plants allow their root systems to process water there, but also to evaporate it when it arrives.
If we take a closer look, we see that the developments do not just serve to beautify the cityscape. Several components enable the quantity and quality of water runoff to be controlled before it enters the existing sewer network.
The memory gap
- A simple cavity in which runoff water collects before it enters the ground.
Open in full screen mode
The ditches near the parking lot catch some of the water runoff.
Photo: Radio-Canada / Claude Bernatchez
Bioretention areas
- They are easy to spot thanks to the horizontal pipes sticking out of the ground and covered with a fence. They are used to store and filter the water that flows naturally into the ground. When the amounts of water are too large to be absorbed by the basin and they reach the top of the screen, they flow into the pipes and follow their path towards the retention chambers.
Open in full screen mode
Bioretention areas absorb and filter rainwater.
Photo: Radio-Canada / Claude Bernatchez
Retention chambers
- Underground cavities that temporarily store excess water before releasing it into the network.
Open in full screen mode
Retention chambers hold back rainwater before it is discharged into the sewer system.
Photo: Courtesy of the City of Quebec
Pretreatment units
- Screens through which water flows before entering the pools and which serve to remove the largest particles carried by surface water.
Open in full screen mode
The sieves are used to sort out the largest particles carried by the water.
Photo: Radio-Canada / Claude Bernatchez
Water tanks for market use
- Reservoirs that collect rainwater, which is used by traders to irrigate their crops and supply market toilets.
The Roland Beaudin car park is clearly innovative, it is a very interesting application in my opinion. […] It’s about following this type of development and learning from it.
Spend money to correct past mistakes
Innovations to improve an aging system come at a cost: $4.6 million to renovate the Roland Beaudin Room.
We are not yet very advanced with benefit-cost analyzes across the entire infrastructure life cycle, says Sophie Desmeules from INRS, but intuitively we think it is cheaper. She adds: If we wanted to replace all of our underground sewer pipes to make them larger, we would have to replace the entire street [alors que refaire] Surface development costs much less.
Another example: the dead end of Boulevard Neuvialle
Engineer Renée Lanthier from the City of Quebec emphasizes the variety of feasible solutions and cites the Neuvialle dead end in the Duberger sector as an example. A road development that includes swales (a ditch) and a permeable paved parking lot under which water can be stored before being discharged into the Saint-Charles River.
Climatological data and precipitation curves that predict future precipitation are used for planning sewer infrastructure. They are updated regularly, but they all point in the same direction: flash floods will become more numerous and more frequent.
Renée Lanthier reminds us that the adaptation solutions that climate change brings are multiple and that the development of the Roland Beaudin car park or those we see along the streets are just some of the tools available. In some places it will be necessary to increase the capacity of underground water pipes, in others we will focus on demineralization of soils or the creation of artificial swamps.
According to Renée Lanthier, city engineer, there are already 251 retention ponds spread across all Quebec districts. In all new districts it is a requirement that the runoff generated by these new streets be diverted entirely into a retention basin. They allow water quantity and quality to be controlled before it is fed into the network.
Open in full screen mode
The retention basin of the Parc de la Montagne-des-Roches in Charlesbourg.
Photo: Radio-Canada / Claude Bernatchez
Like the Montagne des Roches, into which the waters of a district of Charlesbourg flow. They are also positive for biodiversity, remembers Sophie Desmeules. We create an environment based on plants […] it can have an impact […] especially at temperatures during heat waves. In central districts it can be very important.