Ontario Construction News staff writer
The City of Mississauga’s stormwater infrastructure helped to mitigate the impact of near-record rainfall last week, demonstrating its role in assisting with protecting the city during extreme weather events, officials say.
On July 16, Mississauga experienced a ‘100-year storm’ with about 106 mm of rainfall in a few hours – much more than the average 75 mm for the entire month of July. Heavy rains falling in a short period of time caused high water levels and localized flooding on roads and along creeks, rivers and streams.
While some parks flooded, trails washed out, embankments eroded, debris flowed into neighbourhoods, and some residents experienced property damage like basement flooding or water pooling in their backyards, municipal infrastructure “handled the majority of the unusual quantity of rain as a result of its network of underground pipes, designated stormwater ponds, culverts and overland flow routes along roadways”.
Projects funded by the municipal stormwater charge, such as the construction of Lake Saigon—a stormwater management pond at Matheson Blvd E. and Hurontario Street—protected flood-susceptible lands downstream within the Cooksville Creek watershed. These infrastructure improvements were key in mitigating the impact of flooding within the city, highlighting the importance of the stormwater charge as a critical investment.
Last June, council approved its first Stormwater Master Plan, Build Beautiful to refine the stormwater program, management systems, and infrastructure and help address issues facing including flooding, water quality, and pollution while working to preserve our environment.
“With climate change unfolding, we will see storms like this happen more frequently,” officials said. “Every degree of temperature change, even one degree warmer, can impact our environment significantly.
“This could mean more widespread flooding with rainfall levels expected to increase in volume and intensity, with more frequent and intense precipitation. It’s important that we manage stormwater to reduce flooding risk to your property, lower erosion of our creeks and limit the amount of pollution entering Lake Ontario.”
Historically, on July 8, 2013 the city experienced a storm where more than 126 mm of rain was recorded at Toronto Pearson airport over a stretch of 10 hours. Another recorded storm was in 1954 –Hurricane Hazel, which dropped more than 200 mm of rain over Mississauga in 24 hours.
Stormwater infrastructure is sized to convey flows based on “peak intensity.” For example, 50 mm of rain falling intensely over two hours is more likely to cause issues in the urban environment than if 50 mm of rain fell slowly over two days.
Currently, there are more than 1,900 kilometres of storm sewer pipes in its drainage system. If laid out end-to-end, these pipes would connect Mississauga to Winnipeg. The stormwater drainage system also includes more than 51,000 catch basins, 270 kilometres of ditches, 150 kilometres of creeks, and 81 stormwater management facilities (including ponds, underground storage, and Low-Impact Development facilities) that help collect, drain, and clean the city’s rainwater runoff.
The stormwater drainage system is one of the largest assets owned and operated by the City of Mississauga. The 2024 Corporate Asset Management Plan estimated a replacement value of $7.6 billion.
Over the next 10-years, the city’s stormwater program to build, expand, and maintain our stormwater system is fully funded because of the self-funded stormwater charge. However, there is still a need to appropriately contribute to the Pipe Reserve Fund to allow for the future replacement of the city’s aging storm water pipes.
The city is seeking a commitment from all levels of government and is advocating for additional funding to help bridge the infrastructure gap. This is crucial for underlining priorities, such as stormwater infrastructure, that are vital to the safety of our community.