Toronto faces uphill fight with flooding

CITY DENSITY, OLD SEWER SYSTEM LEAD TO ISSUES WITH FLOODING, OBSERVERS SAY

Steady rain and thunderstorm warnings in Toronto on Tuesday had residents bracing for waterlogged streets and transit delays for the third time in as many weeks, with the city saying it was prepared to respond quickly to urgent needs.

The issues the city faces during periods of heavy rainfall are complex, observers said, noting that Toronto’s density and decades-old sewer system are among the main challenges during extreme weather.

“When you have really short intense storms, the rainfall overwhelms our infrastructure capacity and we end up with excess water at the surface,” said Jennifer Drake, a civil engineering professor at the University of Toronto.

Since the beginning of August, more than 148 millimetres of rain has fallen onto Toronto, according to Environment Canada.

“In the past, when it was rural, agricultural and forested, most of that rainwater infiltrated into the ground or evaporated,” said Drake. “We lose those processes as a result of city building and we end up generating a lot more surface runoffs that then turn into flood water.”

Lou Di Gironimo, interim deputy city manager in Toronto, said the sewer system in Canada’s most populous city acts like a “bathtub” and can get overwhelmed during heavy rainfall.

“It works fine if you fill it up with the normal amount of water but if you fill it up too quickly with a hose, it will overload and spill over,” he said.

In order to prepare ahead of a storm, Di Gironimo said the city encourages residents to use Toronto’s basement flooding protection subsidy program, which offers owners of single-family, duplex and triplex residential homes a subsidy of up to $3,400 per property to install flood protection devices.

The city is also allocating $3.1-billion for storm water management, said Di Gironimo.

The money will be split between a basement flooding protection program to improve sewer capacity and a plan to improve the quality of stormwater released to the city’s waterways.

Last year, the City of Toronto Act was also updated to allow green roof bylaws to be passed. A study conducted by the University of Toronto that was published in 2017 showed that green roofs have the capacity to capture an average of 70 per cent of rainfall over a given time, relieving underground stormwater systems and ultimately releasing the rain water back into the atmosphere.