Managing stormwater to improve Canadian cities’ safety and resilience

Adapting to new realities, in a changing climate

The population density in Canadian cities has continued to increase over time. Combined with rising sea levels and unpredictable precipitation, the pressure on municipal infrastructure to manage excess water has been increasing. Stormwater infrastructure plays a critical role in helping to prevent urban flooding. By studying how it performs during extreme storms, engineers can provide advice to help local authorities adapt their infrastructure and mitigate losses from flooding.

In this context, the City of Toronto worked with researchers from the National Research Council of Canada (NRC) who have technical expertise in infrastructure resilience supported by well‑known, unique testing facilities. The objective of the project was to study how increased rainfall behaves on Toronto streets and how efficiently the existing infrastructure diverts water into the storm drainage system.

Recreating roads inside the testing facilities

Researchers from the NRC's Ocean, Coastal and River Engineering and Construction Research Centres worked together on this project as part of the Climate‑Resilient Buildings and Core Public Infrastructure (CRBCPI) Initiative, and with funding support from Infrastructure Canada and the City of Toronto. Since 2016, the NRC has been working to develop decision‑support tools such as national model codes, guides, standards and climate design data to help ensure buildings and core public infrastructure are designed and built to withstand the effects of climate change in Canada. In fact, the idea for the project arose from a workshop that the NRC organized with municipalities to identify research needs.

With expertise in adaptive and sustainable engineering solutions, and in structural and coastal resilience, the NRC has been supporting the development of technologies to mitigate the impacts of weather extremes and climate change, including flooding from coastal and inland sources.

At the NRC's Coastal wave basin research facility in Ottawa, NRC experts built a physical model of the City of Toronto's road infrastructure, using wood and tar paper. With a water pump and a flow straightener, they recreated several scenarios from typical light rain conditions to heavy rains and even extreme flood conditions. Through testing, researchers evaluated the infrastructure's ability to capture the water under various flooding conditions.

"It's always rewarding to help our clients answer important questions that allow them to make key decisions. It's also interesting to "play" in the lab and see what it's like to throw 1 ton of water on a roadway every 2.5 seconds. It's like having a waterfall running through your office," says research council officer and project manager, Louis Poirier.

Choosing the right grates for the best results

To manage this water and prevent overland flooding that can lead to basement flooding, surface grates and catch basins on the street play a crucial role. As the only visible part of a much larger infrastructure system, surface grates and catch basins collect stormwater (rain or melted snow) from streets and move it through a complex underground storm sewer system. The stormwater eventually flows into the environment—normally a river, stream or lake. Although all surface grates and catch basins serve the same purpose, which is to move stormwater off the roadway, each surface grate model offers unique advantages, suited for different results. Some of the common catch basin grate patterns residents may see while walking in their neighbourhood include the herringbone pattern, a square grid, or parallel rectangular bars. To aid drainage, the grates are often placed near intersections and along low points in the roads. Residents can help reduce flooding by keeping them clear of leaves, debris, and snow.

Using wave gauges to calculate the amount of water on the model road surface, the research team determined how much water was removed from the roadway for each catch basin in various conditions. Data was collected for numerous scenarios, including various surface grates pattern styles and different incident water depths. The results gathered from the testing phase will help the City of Toronto and other Canadian municipalities improve the numerical models of their storm drainage system, to better meet the challenges of managing extreme rainfall events.

"We're looking forward to reviewing the data from this research and applying it to the City of Toronto's ongoing planning and future stormwater management and basement flooding‑prevention projects. Thank you to the team at the National Research Council of Canada for your scientific and technical expertise, and for working with us on this exciting and innovative project," says Jennifer Spence, Project Manager with Toronto Water who, together with Senior Engineer Tom Dole, led this study for the City of Toronto.

Working together to make cities more resilient for all Canadians

With a changing climate and increasing urbanization, municipal authorities will need to continue to adapt to new realities. A better understanding of their existing infrastructure's performance will support informed funding decisions when it comes to expanding, upgrading or replacing existing systems. Planning for severe weather events and using prediction tools and physical testing of novel infrastructure will lead to improved flooding preparedness and resilience.

With infrastructure being the backbone of modern society, the federal government is investing to modernize Canada's infrastructure to ensure that it is sustainable, inclusive and resilient for future generations. As part of its Departmental Sustainable Development Strategy 2020 to 2023, the NRC is committed to supporting the federal sustainable development goals through research towards modern and resilient infrastructure. This project realized with the City of Toronto and the NRC will help Canada create safer and more sustainable environments for all Canadians.