For anyone who thinks Toronto’s aging sewer infrastructure was to blame for Monday’s flooding, University of Toronto civil engineering professor Bryan Karney has some words of caution: No system could handle the amount of rainfall the city saw that night, which outdid even 1954’s Hurricane Hazel.
Prof. Karney, chair of his department’s division of environmental engineering and energy systems, agrees that changing weather, brought on by global warming, means cities have to take a hard look their water infrastructure. But over all, he says, Toronto has handled the onslaught fairly well.
Does how we build our sewer systems, and how we manage water in this type of event, need to change in light of climate change?
Climate change is probably going to have to force us to rethink that. But it’s very difficult to go from a single event like even the severe one Monday and say that’s definitively climate change. The world can throw stuff at us that’s just statistically anomalous, even under a stable climate. The reality that we really have is that nature can throw stuff at us that’s way, way, way beyond our capacity to deal with in ways that are completely without disruption.
So even if we spent a Cadillac amount of money and redesigned our sewage systems to take more water, we would inevitably still come up short?
When we have minor events, routine rainfalls and snow-melt events, those are the ones that are designed to go in the storm sewer systems. We can afford those pipes. They are big pipes, and they are used infrequently but they’re manageable and they are economic. But what you require to handle more extreme events, the Hurricane Hazels of the world, are pipes that are so humungous that they’d take the whole GDP of Canada to outfit a single city. They’d be a capacity that would almost never be used. [It would be like] designing every facility in Brazil for the World Cup.
Do we risk going too far the other way and under-designing things because we are cheap?
What we have to look at is the incremental cost of protection versus the damage that’s caused by the occasional extreme event. And what we really should be doing very effectively is designing the systems that take the water when the minor system fails. And so we design what’s called the major system, not just the pipes, but we design the roads to be water-conveyance systems. That’s what saved us from catastrophe. By and large the system managed a remarkably severe event without major catastrophe.
And that’s why most of the flooded roads across the city were by Tuesday free of water. They were designed that way?
A great many of the roads carried it and people were almost unaware of the fact that there were several inches of flowing water on the road. It just looked like a heavy rain. But the reason there was that water on the road was the sewers at that point were probably full or blocked. Really, we managed it remarkably well, which meant that the major system by and large did its job.