High-rise builders flagged in new flooding insight

Monday, August 31, 2020

It may come as no surprise to learn that Toronto is experiencing more flooding. The city’s labyrinth of sewage and stormwater pipes was not designed for the modern era and it’s going to take time, money and commitment to fix the system.

That’s the assessment of Patrick McManus, executive director of the Ontario Sewer and Watermain Construction Association, and Dennis Cancian, executive director of the Ontario Formwork Association, who were guests on a podcast entitled The Big Pipe – Project Plans for the Future that was released by the Residential and Civil Construction Alliance of Ontario (RCCAO). It is the eighth installment in a nine-part series, called Conversations About Construction, that deal with issues affecting construction.

A big part of the problem, they noted, is that the system was built for a different era and, over the years, very little has been invested in underground infrastructure to increase capacity.

“We have what is referred to as a combined sewer system in Toronto and that is putting both household sewage and stormwater into the same pipe underneath roads,” says McManus. “In newer cities those things are built separately and are diverted into different pipes and it makes it easier to manage peak flows. But in Toronto the sewer system is designed on a very, very old model. “It’s a system that’s inevitably prone to flooding, particularly as the city grows vertically and capacity of the sewer system becomes more strained.”

Issue of particular concern for high-rise builders

Cancian says the issue is of particular concern to builders of high-rise towers in downtown Toronto because they typically have parking garages that go down six or seven storeys and are subject to flooding if a severe thunderstorm overwhelms the system with a large amount of rainfall.

“They never envisioned having these big storms and having the issues that they’re having now, and I don’t think they actually envisioned the density that they’re getting now in the downtown area.”

Cancian notes that builders have begun making the case for above-ground parking in new high-rise developments, which would also ensure that underground aqua flows are not disrupted by developments.

The guests noted that while the city has embarked on a multi-year plan to build a 22-kilometre-long tunnel system that will enable billions of litres of sewage and stormwater runoff to be captured, getting the system in place won’t be easy as the population is growing and building continues.

“We’re growing the sewers at the same time we’re experiencing development,” says McManus. “The sewer system is supposed to be planned out before development. Instead we’re doing these things concurrently.”

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