How do we solve the problem of urban flooding?

Scott Sutherland

Although residents of Calgary and Toronto would certainly say that we have a problem with urban flooding, the statistics that governments rely upon for these sorts of things paint a less-urgent picture. With the flooding in Calgary deemed a 70- or 100-year flood, and the Toronto storm already being dubbed by some as a '100-year event', does it make sense to rush to address the flood preparedness of our cities if we can't expect another event this century?

Actually, it probably does.

The tricky thing about those 'X-year' historical designations is that they're based on, well, history. Which makes a good deal of sense when you expect conditions in the affected area to remain the same and, to be fair, is the only approach that's made sense for us in the past. However, our changing urban landscapes, to say nothing of our changing climatic environment, mean that what we've relied on in the past isn't going to serve us well in the future, and Canadians would likely be better served to look at these cases as a taste of things to come rather than a once-in-a-lifetime event.

[ Related: Toronto flood highlights the challenges of severe weather forecasting ]

The first 'prong' of the problem — the one that we have a better chance at directly influencing — is the infrastructure of our cities.

The Federation of Canadian Municipalities Infrastructure Report Card, released last year, rated the physical condition of the network of wastewater and stormwater systems as 'adequate to very good', which sounds very promising and doesn't at all explain why Torontonians were, in some cases, neck-deep in water or trapped in swamped trains on their Monday evening commutes. The issue, according to Paul Kovacs, of the insurance industry's Institute for Catastrophic Loss Reduction isn't so much the condition but the facilities themselves.

Speaking to CBC News, Kovacs said, "In municipalities across Canada, outdated storm and waste water infrastructure has resulted in increased flood damage to homes and these types of situations will likely get worse in the near future," and that, "the infrastructure we count on to prevent floods is not enough to do the job."

Part of the issue, according to designers and engineers familiar with topic, is that some of our biggest municipalities rely on 19th-century solutions to a 21st-century situation.

Jane Wolff, of the University of Toronto, told CBC News, "The logic of 18th- and 19th-century engineering was to get water away from buildings and structures as quickly as possible. So roofs and streets are made from impermeable material and water is funneled into drains towards an end point like lakes and rivers."

When your city gets as big as Toronto, with its miles of paved surfaces, you have to funnel that water a long, long way to get to its end point. And along the way — as drivers found out this week — there are a lot of places where the funneling breaks down, especially when the system is being inundated with a month's worth of rain over the course of a few hours.

Wolff suggests so-called 'soft engineering' is an integral part of the solution. She points to "green roofs, porous parking lots and increased numbers of trees" in urban areas as a piece of the puzzle, allowing open portions of earth to absorb water that would otherwise run-off or pool somewhere in our concrete jungle. Typically used to reduce erosion along shorelines, soft engineering calls for the introduction of vegetation to support and stabilize traditionally-engineered structures and areas. Adding more greenspace to our towns and cities has other obvious benefits, of course, and features like roofs with vegetation have been lauded in other situations for their environment-friendliness.

Some good news on this front came in the 2013 federal budget, that earmarks over $53 billion in infrastructure investments, although that includes investments in everything from roads to military bases, so what may be aimed at waste- and storm-water networks remains a question mark.

If such flooding events seemed destined to remain once-per-century or so occurrences, then it might not feel like action beyond that is warranted; we'll make some investments and gradually redesign sewers and drainage systems that have been serving cities like Montreal for the past 250 years. Except, there's other 'prongs' to this problem.

You probably know what's coming here... because it comes up a lot when we talk about the country's environmental future, and with good reason. What, exactly, will the country's climate look like in 250 years? Or 100? Or even 50 years, for that matter? If we can expect significant change to our weather patterns over the next 50 years, then suddenly betting on a 200-year-old sewer system and a '100-year storm' doesn't seem quite as safe, does it?

Released in 2009, the U.S. Global Change Research Program's Second National Climate Assessment draws from a variety of sources, including the famous IPCC report and provides us with an overview of the forecast of 15 different climate models for the continent's future precipitation.

The hatched areas on the map indicate where confidence in the changes is highest. As you can see, the projected changes over most of Canada for fall and especially winter and spring lean toward higher confidence, wetter (in some cases, much wetter) weather toward the end of this century, with more precipitation expected in the form of rain than snow.

The report's findings also include the news that "Heavy precipitation events will likely be more frequent. Heavy downpours that currently occur about once every 20 years are projected to occur about every four to 15 years by 2100, depending on location."

So much for relying on our '100-year storm' projections.

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Now that we're all good and depressed, what can we actually do about this?

One thing it seems that we're already primed for is just simply to put pressure on our leaders to address the problem. It will undoubtedly be expensive to refit major (and even smaller) cities' sewer systems, but it seems like we're already overdue on that front and as the population and paved areas swell, we're going to run out of borrowed time, with or without climate changes getting involved.

At a closer-to-home level, helping your neighbourhood along by engaging in some of that soft engineering — say, exchanging your patio for a greenspace — is a possible avenue. The Institute for Catastrophic Loss Reduction has a list of items you can address to help avoid basement flooding (apparently the most costly of all the damages reported).

If you'd like to read more, University of Toronto Professor Jennifer Drake, who's an expert on the issue of Low Impact Development — managing stormwater as close to the 'source' as possible — offered her insights on the flooding and what we can do, earlier this week.

(Image credits: Frank Gunn/The Canadian Press, USGCRP 2009)

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