Avert Magazine

Reflecting on the devastating 2013 storm, Mississauga takes lead in municipal flood resilience

August 1, 2023
By Local Journalism Initiative

By Rachel Morgan – Local Journalism Initiative Reporter & Paige Peacock

It’s been a decade since the 2013 flood that caused widespread damage across Mississauga, Brampton and many other parts of the GTA. After a brief early evening deluge, water overtook the streets and corridors of concrete-covered municipalities, creating traffic chaos, flooding basements and overwhelming creeks and riverbanks. It also left elected leaders questioning how prepared their cities really were for a major flood event.

A forecast issued by Environment Canada at 8:11 a.m the morning of July 8, 2013 predicted a 40 percent chance of evening showers with a risk of thunderstorms in the afternoon and early evening. Five hours later, a special weather statement was issued at 1:31 p.m. advising that “local heavy downpours giving 30 to 40 mm of rain in less than one hour are likely.” By 5:51 p.m. that day, a severe thunderstorm warning that included Mississauga and Brampton and other parts of the GTA was issued.

The ensuing torrent came down like a waterfall, flooding the Dixie Road underpass as residents worked to redirect traffic. It wiped out guard rails and drenched basements – causing extensive damage to thousands of homes as large amounts of water with nowhere to go rushed from concrete roads, sidewalks and driveways, into stormwater systems that were completely overwhelmed. The water made its way into low-lying basements and others that were either deluged by backflow or failed sump pumps that could not do their job when the power went out early in the storm. Roads that suddenly looked like lakes were closed, people relying on public transportation were left stranded and city stormwater systems could not keep up with the volume of water that fell. It was the costliest storm in Ontario’s history, causing $932 million in damages.


A year later, a 2014 report by Amec Environment & Infrastructure Inc. included a Toronto Region Conservation Authority (TRCA) water gauge reading near Toronto Pearson Airport that had shown 138 milimetres of rain fell in about 10 hours. Between 1981 and 2010 climate data from the Toronto Pearson weather station showed the area sees approximately 681 milimetres of rain annually – meaning the 2013 storm dumped about a fifth of the city’s yearly rainfall in a single evening.

According to the federal government, a “Heavy Downpour” in Ontario is defined as 50 milimetres or more within one hour, which triggers a warning through Environment Canada. The maximum rainfall in one hour on July 8, 2013 was 79 milimetres.

A decade later, as a result of the warming climate, extreme weather events like the 2013 storm that previously occurred once in a century are becoming more and more common. The rapidly increasing temperatures witnessed around the world (July will be the hottest month ever recorded globally, according to Leipzig University in Germany) will continue to set the wrong types of records, as municipalities struggle with more extreme weather events, natural disasters and all the fallouts from what were once rare atmospheric anomalies. Scientists have been warning of this new reality that has now arrived, for decades.

It has created a new level of planning for municipalities where the worst impacts of our changing climate are felt immediately.

A growing list of questions is being wrestled with: how much capacity do municipal stormwater systems need to handle, and how will the massive replacement costs be covered; how should new residential developments be designed to withstand extreme heat and all its effects; what type of energy systems should municipal buildings use; how can more permeable materials be deployed to build city streets and parking facilities; what safeguards, such as residential back-flow valves and basement sump pumps, would best prevent future flooding; how do emergency and disaster preparedness plans need to be changed to keep all residents safe?? The list just keeps getting longer.

Perhaps the most pressing question is: Who will pay the billions and billions of dollars needed to protect cities and towns from the coming weather?

Managing stormwater is especially crucial in Mississauga.

The 2013 flood was eye opening for residents, many of whom had not experienced such a disaster before. It kickstarted a suite of changes to the city’s system of stormwater pipes, spillways and sewers, all designed to capture and redirect stormwater to treatment facilities before being pumped into Lake Ontario. In an email statement to The Pointer, a City spokesperson said the flood “reinforced the City’s need to formally maintain and increase investment in our aging stormwater infrastructure,” which included interdepartmental collaboration to make flood prevention a top priority.

In 2021, the City implemented its Climate Change Action Plan which detailed efforts for mitigation and adaptation. One of the actions required the City develop a Stormwater Master Plan to oversee the enhancement of flood resilience across the municipality. It outlines 22 actions with recommendations for managing stormwater in the short and long term.

“The City of Mississauga is committed to protecting the quality and integrity of water through each stage of its cycle, to provide clean and safe drinking water for current and future generations, to protect the local and global environment, and to mitigate and adapt to a changing climate,” the plan, which was published in May, details.

It is another step in the right direction for a municipality to adapt to the changing landscape and risks associated with climate change. The city’s unique location on the edge of Lake Ontario is an added risk as its rainwater and snowmelt runs down and into the Great Lake, the source of Mississauga’s drinking water.

“We have all these sorts of changing risks that we need to make sure that our plans for infrastructure are going to be as resilient as possible,” Jennifer Drake, a professor of civil engineering at Carleton University, says. “When it comes to our stormwater infrastructure, making sure that we have plans that are in place, especially with urban flooding, it’s a whole system, and so you need to have infrastructure that’s got redundancies in it 1/8and 3/8 a pathway so that if one system fails, there’s still another pathway for the water to work its way through the urban environment.”

These redundancies, or `Plan Bs’ are crucial as climate change alters the frequency and variability of storms, making extreme weather events harder to predict and prepare for. The Region of Peel is warming at twice the rate of the global average and the dramatic temperature increase, mixed with the proximity to a large body of water, creates a perfect storm of impacts.

The City estimates the worst one percent of extreme precipitation events will be five percent more common by the end of the decade. But by the 2080s, the same worst one percent will be 90 percent more common, with an annual increase of 99 millimeters of rain.

Due to its topography and concrete design – which doesn’t allow water to absorb into the ground during rainfalls – Mississauga is particularly vulnerable to these types of extreme weather events. The city, and its Credit River Watershed, are situated in the middle of a basin that begins around the northern headwaters, runs south through the Greenbelt and down into Lake Ontario. Five major watersheds exist within Mississauga, including: the Credit River, Humber River, Etobicoke Creek, Mimico Creek and Sixteen Mile Creek.

Keeping stormwater infrastructure in good working order is the weak link for many municipalities, Drake explained. Municipalities need to ensure they have the processes to keep existing infrastructure functioning through an extreme weather event. This can be done through inspections, cleaning, and making sure catch basins are free of debris so water can enter the pipes. She emphasized the importance of understanding what we expect of our stormwater infrastructure and using that to determine what kinds of updates are needed to address a rapidly changing environment.

“What we expect of our stormwater infrastructure has continuously evolved. Today, we don’t just want our stormwater infrastructure to capture and move the water as quickly as possible. We have a lot of other things that we actually want it to do for us,” she said. “We are concerned about the water quality, we’re concerned about erosion, we’re concerned about urban habitat, and so I think those changing objectives have meant that the infrastructure has to evolve as well, so that it can be multifunctional.”

It is crucial for municipalities to understand the changing requirements of stormwater infrastructure while simultaneously ensuring the same infrastructure is capable of handling increased capacity demands with a changing climate. Much of the infrastructure that was built over the past five decades will not be able to handle the volume of precipitation we are now seeing. But technologies have been rapidly evolving over the past couple of decades which have created better options for municipalities to deal with increased runoff.

The City of Mississauga is starting to focus on the addition of green infrastructure, outlined in the Stormwater Management Plan. This is increasingly used by already built-out municipalities.

“What 1/8green infrastructure 3/8 means is that you can learn from nature and mimic nature to control the volume of water and then keep the water clean, too,” Cheryl Evans, director of flood and wildfire resilience at the Intact Centre for Climate Adaptation at the University of Waterloo, tells The Pointer.

Examples of green infrastructure include permeable pavement, which allows water to seep through and slowly drain into the groundwater; lining roadways with small creeks and berms to redirect water flow away from hard surfaces; and green roofs that collect water while contributing to the tree and shrub canopy in the city. Evans says green infrastructure often serves dual purposes, helping to capture and direct water, while also increasing native plant cover and contributing clean oxygen back to the atmosphere.

One key adaptation seen across southern Ontario in collaboration with conservation authorities is the renaturalization of streams. In the mid-20th century, rivers and creeks were straightened to streamline the flow of water. As education and technology evolved, engineers realized these straightened streams were actually causing more harm and increasing the potential for flooding.

“Starting in about the `90s, what they started realizing was that you’re actually getting water off the land faster. And because it’s not moving slowly, it’s starting to increase erosion and starting to increase pollution. And it’s starting to cause flooding, because you don’t have as much area for that creek to move,” Evans says. She is excited about the promise of renaturalization across southern Ontario.

Mississauga is built out to its limits, with no more greenfield left. With the only option left for growth lying inside already urbanized areas, Drake says having green infrastructure is particularly crucial in high density cities, like Mississauga, where greenspace is scarce.

There is a balancing act when considering which types of materials to use when designing all the features of an urban centre, alongside the natural topography and geography that does a much, much better job of controlling atmospheric impacts. Streams will start to exhibit “urban syndrome characteristics,” meaning evidence of impairments or changes to the flow of water when as little as 10 percent of the surrounding area is impervious, meaning paved over or covered in concrete where water cannot seep through.

“So it really is a very small amount of development that causes observable changes in receiving water or natural environments,” she says. But it’s not practical or realistic for cities to live in only 10 percent of an area and keep the remaining land undeveloped. In Mississauga, only 12 percent of land is greenspace, while the rest is made up of mostly impervious surfaces (the City has done work to introduce materials for roads and parking lots that are more impervious than traditional concrete and asphalt).

“The difficult choice that we have as society and regulators and developers is balancing the needs of our communities with the needs of our environments, and making sure that we have that we do what we can to support and protect and identify what ecosystem functions are critical,” she explains. “When we build with low density, you inherently are exposing people to risks because we know the risk of these weather events are small and isolated, and if we occupy a larger and larger area of land, it’s inevitable that someone’s going to be exposed to that extreme weather.”

Low density growth and sprawl, Drake says, can have potential risks associated with them, as opposed to concentrating urban growth and development so that municipalities are not stretched outward with infrastructure that needs to be maintained over a far greater space. She says we all have to learn to live with less space.

While Drake details the shortcomings of sprawling communities, Evans says regardless of how communities are built, climate change will have an impact, and nature will prevail. Now, these natural consequences are being partly driven by human activity.

“Every city is going to be a little bit different, but in general, there are going to be areas within every city that are going to face flooding.”

Municipalities need to classify each particular area according to its unique geography and urban design in order of priority, to plan and construct the most effective infrastructure to mitigate the impacts of climate change.

“It’s a delicate dance, you have to figure out where the priority projects are, because there’s finite money, but also what is the level of support in the community for these particular projects.”

In 2021, Mississauga’s stormwater infrastructure was valued at $5.3 billion. The City’s intricate drainage system consists of 1,911 kilometres of sewer pipes which, if they were spread in a straight line end to end, would reach all of the way to Winnipeg. The maze also includes 270 kilometres of ditches, 150 kilometres of creeks and 52,000 catch basins, all of which drain into Lake Ontario.

It would be impossible to update the entire system simultaneously which is why municipalities have to decide which projects will have the most impact first. In 2022, the City had a stormwater operating budget of $44.6 million. By 2025, the City estimates this will increase to $47.3 million, an increase of about one million dollars a year.

Dealing with insufficient funding for repairs is not something that is unique to Mississauga. In May, the Toronto and Region Conservation Authority (TRCA) released a report that said more funding from the provincial government was needed to upkeep its flood prevention infrastructure (dams, dikes, berms, etc.) which was aging and badly in need of repair. The report outlined 14 projects for maintenance and enhancement of flood infrastructure with an estimated total cost of $34 million. Despite six of the projects being labelled high priority, only one is currently fully funded, two are partially funded, and the remaining 11 are unfunded.

“It’s a really tough process to figure out what’s the highest risk? Where’s a priority for funding money, etc?” Evans says. “For example, if you’re a municipality, you really, really, really want to make sure that if there is a big flood, that the road in front of your hospital, and your hospital itself does not get flooded. Every municipality is different. And they have to make a plan based on where their risks are, what their priorities are for their community, and, and what they can afford.”

Despite the uncertainty of climate change, the City of Mississauga says it is prepared to take on challenges that are inevitable.

“We feel confident that the steps we are taking are the right things to be doing to mitigate the risk of flooding,” the City told The Pointer in an email statement. “However, weather is and always will be unpredictable and no municipality can ever guarantee that flooding will never occur again. The City will continue to undertake studies and invest in capital projects to increase our resilience.”

Drake says Mississauga has been a leader in the province with its customized stormwater charge, a city-wide initiative that was implemented in 2016. It costs homeowners based on how big their property is (larger properties with more covered land for homes and driveways pay more because they send more stormwater into the municipal system instead of the ground) and creates a revenue stream so the City has the resources available to invest in new infrastructure or operations maintenance. The uniquely Mississauga plan was hailed by municipalities across the country, for creating a disincentive to live in larger properties, and for charging each homeowner their fair share to cover the costs of their own stormwater burden, instead of having property taxpayers with much smaller houses subsidizing others who create much more of the runoff.

The City’s spokesperson said revenue collected is used exclusively to deliver stormwater services and programs, to meet the increasing demand and investment for stormwater management, including planning and operations, new capital construction and improvements/repairs.

Drake says there is currently a lack of education for residents – the Stormwater Master Plan only governs city-owned property. This education includes developing an “integrated system” that addresses practices and procedures to protect the public, and the private property of residents. Recommended mitigation and adaptation strategies such as how to use downspouts, catch barrels, sump pumps and backflow valves can save homeowners thousands of dollars in the long run.

In March, Liberal MPP for Beaches_East York, Mary Margaret McMahon, tabled a private members bill encouraging provincially legislated flood resilience education across the province. Bill 56, as it was called, aimed to properly educate homeowners on ways they can protect their own assets from the increasing risk of storms and flooding.

“Bill 56 is a win for everyone. It’s not a partisan issue. It’s a win for insurers. It’s a win for renters living in the basement ? It’s a win for homeowners, it’s a win for municipalities and it’s a win for the government. There is no downside to this bill, whatsoever,” McMahon said at a press conference in March.

Despite her confidence in the Bill, it was voted down by the PC majority government, claiming flood resiliency should be left to conservation authorities which have the most experience on the topic. Six months earlier the PCs slashed the mandate of conservation authorities, limiting their ability to comment on development applications and making it easier to build in flood plains.

A 2022 audit by Ontario’s Auditor General Bonnie Lysyk found the provincial government was utterly failing in its efforts to protect Ontarians from flood risk. Evans says she still believes municipalities have the power to work with other governing bodies to protect their residents from flooding.

“We are trending in that direction. It’s becoming more popular. But if you are an engineering firm, you need clear guidelines, design guidelines. And you need to meet minimum standards provided by the province.”

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