October 17, 2014 6:33 pm
Updated: October 17, 2014 6:38 pm

Why Toronto keeps flooding and which basements are most at risk

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WATCH ABOVE: Sean O’Shea explores why parts of the city keep flooding after rain storms. 

TORONTO – Whenever there’s a severe storm in Toronto it seems residents across the city deal with flooding.

“I think the public is becoming more aware,” said Laurian Farrell, senior manager of flood risk management at the Toronto Region Conservation Authority (TRCA).

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“People are sharing their stories, people are tweeting their pictures of basement floodings whereas before we might not have heard about it.”

So why is the city flooding? Infrastructure plays a role.

“From our flood records. It might be two to three times in the summer that we’re getting these types of the events. It’s really less than 5 per cent of all of the storms that we get are causing the problems, but there’s such huge impacts that it seems like we’re getting them more,”  Farrell said.

“These short thunderstorm, severe weather events overwhelm the infrastructure, so the storm sewers and road networks that are built to move storm water are overwhelmed because it’s just the speed of the water coming at them.”

READ MORE:  Heavy rain washes out GTA streets, disrupting TTC service

According to Toronto Water, the city is experiencing more severe weather events with more rain over a short amount of time.  The extreme weather increases pressure on the sewer and road drainage system, which can become overloaded, leading to surface and basement flooding.

WATCH: Alex Walker from RSA Insurance takes the opportunity to explain how you can protect your home and car from water damage.

There have been four storms which Toronto Water has identified as having a considerable impact on residents:

  • On May 12, 2000, a storm produced an average of 68 mm of rainfall, ranging from 41 mm to 73 mm, depending on the location within the city. This event generated more than 3,000 basement flooding complaints.
  • On August 19, 2005, a storm lasting three hours produced up to 153 mm of rainfall. This storm resulted in more than 4,100 basement flooding complaints.
  • July 8, 2013 Toronto received more than 100 mm of rain within a period of 90 minutes resulting in almost 4,800 basement flooding complaints being reported to the City.
  • June 25, 2014 a storm produced as much as 79 mm within a period of a few hours. This event generated approximately 370 flooding complaints.

TRCA has identified 42 priority areas for flood mitigation. Fifteen of which are within the city of Toronto.

“These represent areas with the highest concentration of flood vulnerable structures within the floodplain, or areas with fewer structures that are subject to the most frequent flooding from the river,” said Farrell.

But as all storms are different, so is the area of the city which is impacted.

“During the May 2000, and August 2005, storms, the majority of basement flooding complaints were from the north part of the city, where the heaviest rains occurred, whereas during the July 2013, storm, most basement flooding complaints were from the west part of the city,” Ellen Leesti, a spokesperson for Toronto Water said in an email.

“Locally intense storms were also experienced in 2008 and 2012, in the south district and east district respectively. It is difficult to predict when and how the next extreme storm will impact Toronto, but it is reasonable to expect that it could hit any part of the city or multiple parts of the city at the same time.”

TRCA officials warn residents to be on alert when severe weather strikes.

“It’s important for people to be safe and to not underestimate the power of water when they see flooding,” said Farrell. “they feel safe in their cars but they really should not drive through water because often the roads are washed out underneath the water.”

Farrell encourages people to call the city of Toronto’s 3-1-1 service line and report a flood.

“That helps the city plan. And they should be aware that any water could be contaminated with sanitary sewage from the sanitary system.  Before they try to go in and clean up themselves.  Research and get professional advice on what to do in their homes.”

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