Wanted: New, and new generation, storm water infrastructure for Canadian cities

0 April 24, 2014 at 3:51 pm by

Though we have to be careful about attributing the rise in disaster losses in the country solely to the poor state of public infrastructure (there are many other factors that have to be considered as well), there can be no doubt that the condition of our built environment plays a major role in the increasing amount of damage from severe weather that we have been experiencing.

In fewer places is this more true than on the storm water management front.

In many cases, older, crumbling, low capacity (and often combined) sewers built to handle 1 in 5 or 1 in 10 year rainfalls have to be replaced with new higher capacity systems. (The scientific and engineering consensus calls for  10 to 15 per cent increases in design standards to account for climate change. One study calls for a more than 30 per cent increase.)

There are, however, several reasons why simply replacing older sewer systems with newer, higher capacity systems won’t be the silver bullet that will solve urban/basement flooding problems in Canadian cities.

A big reason why new sewers may not end basement flooding is that often times the problem causing the flooding is on the homeowners lot (i.e. the ‘private side’), having nothing to do with public infrastructure. I will leave this topic for another day.

Another big reason why new sewers won’t be a panacea is that there will always be that storm that exceeds design and overwhelms the system. This is why we need to discuss not only conveyance of storm water (i.e. the pipes), but also temporary storage of storm water, something that is lacking in many places in the country.

So, while we need to address the issue of replacing old storm water infrastructure, we must also address the question of what I call ‘missing’ infrastructure – those things that never where there in the first place.

Storm water management 101

Storm water systems are typically divided into two parts: the minor system (i.e. the pipes, catch basins and other hard infrastructure located underground) and the major system, consisting of overland flow routes and storm water storage sites that use the surface of the earth.

Up to about the early 1960s in Canada, storm water in cities was managed solely through the minor system (and frequently through combined sewers, i.e. systems where storm water and sewage is conveyed through the same pipe). It wasn’t until after this time that we began to also use the surface of the earth to convey and store storm water. This combined use of the major and minor systems has helped ensure that newer areas of cities and suburbs are often (though not always) better equipped to handle large rainfall events.

And therein lies a big part of the urban/basement flood problem: Older neighbourhoods in older parts of cities don’t just have aged (often combined) low capacity sewer systems, but they don’t use the major system. What’s more, because many cities in Canada are ‘built out’ (i.e. they have no more greenfields to develop), there is very little – if any – room to retrofit in overland flow routes and surface storm water storage sites. So because of the sheer lack of real estate, and density of values, while retrofitting overland flow routes and temporary storm water storage into older parts of cities is not impossible, it is very difficult.

But there are always ‘workarounds’.

On the conveyance side, many cities have taken to using streets with higher curbs and bigger or more catch basins to move storm water and keep it away from buildings (and basements!). On the storm water storage side, cities such as Hamilton, Toronto and Ottawa, Ontario, have taken to installing underground storage tanks to hold large amounts of rainwater to prevent storm sewer systems from becoming overwhelmed. (As the director of the water department of a major Canadian city once said to me “All we have to do is buy a little time – 15 minutes, a half hour – just to let the storm system catch up.”) These tanks have been installed under parks and school football fields and other places. Once completed and grassed over, it is nearly impossible to tell they are there. These tanks have the added bonus of preventing overwhelmed combined or partially combined sewer systems from  releasing untreated water into natural waterways.

While many Canadian cities have shown innovation with the use of storm water retention tanks and so on, a good deal more innovation on the storm water management side is going to be required going forward. This is where we need to initiate a discussion about developing and using a new generation of ‘soft’ storm water infrastructure.

Along with replacing existing storm water infrastructure with more up-to-date, separate, higher capacity systems, and using such solutions as underground storm water storage tanks; we also need to consider the use of bioswales, rain gardens, permeable payment, green roofs, high capacity rain barrels and so on. These can easily be the subject of a separate blog post of their own.

Along with hard and soft infrastructure, we must also foster the spread of certain public policy tools that are currently in place in just a small number of municipalities across Canada. Such tools include bylaws making downspout disconnection mandatory (see Toronto and Markham, Ontario for examples), and the use of storm water credits that encourage less use of pavement and more use of grass and permeable pavement (see Victoria, B.C. and Kitchener, Ontario). These, too, can easily be the subject of a separate blog post of their own.

The storm water conundrum is a huge challenge for virtually every city in Canada and it is clear that there is no single solution to the problem.

What is needed is a whole suite of solutions that can be used in tandem.

Taken together, cities will better be able to manage the storm water we get today, and the greater frequencies and intensities that we will get in the years ahead.

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