September 3, 2010

Column | Korky Koroluk

Storm building on urban runoff

As cities grapple with tight budgets, and as a changing climate begins to force changes in the way our cities must be managed, we hear more about higher urban densities, infill development, smart growth and the new urbanism.

They’re all a part of the same thing, though: An awareness that our cities are unsustainable as they are now. They occupy too much space, require too many roads, and pollute our environment. It’s a constant stretch to provide the services needed to support the rapid urbanization we’ve experienced since the Second World War.

So it was a treat to chat with Dixon Weir recently about a good-news story. He’s general manager of environmental services for the city of Ottawa, and we were talking about a couple of local water projects that have been postponed because Ottawans are using less water, and less dirty water is going to the city’s sewage treatment plant.

Science tells us that among the manifestations of climate change will be changing storm patterns, with fewer small storms and more big ones — and the big ones are likely to be really bad. That led me to ask Weir if the city is looking at the possible need to build bigger storm sewers.

It is a concern, he said. The problem is while we can see a trend, nobody has yet been able to put numbers to it.

We know what we can expect from a 100-year storm, but should we be building for a 150-year storm? And how could we put numbers on that storm?

So, Weir said, since new numbers have not yet been established, the city is trying to design some redundancy into its infrastructure, hoping to be able to recover quickly in the event of a storm that’s really, really bad.

Stormwater management isn’t as simple as just laying down bigger pipes, of course. It involves a lot of the ideas incorporated under the umbrella of “smart growth.” That means capturing rainwater where (or near where) it falls. Green roofs help with that. So do swales, constructed wetlands, stormwater management ponds, less ground-level parking, streets without curb or gutters.

When less stormwater runs off, more finds its way into the groundwater, which is purified as it works its way toward creeks and rivers and lakes. More of it goes to recharge aquifers instead of running down to the sea.

I’ve run across a recent study showing that a one-inch rainstorm on a one-acre meadow would produce 218 cubic feet of runoff, while a parking lot the same size would produce 3,460 cubic feet.

And what is in the parking lot runoff? All the stuff that’s found in gasoline, grease and oils, antifreeze, brake linings and rubber. That means cadmium, copper, lead, zinc, nickel, cobalt and iron.

The study also mentions that because streets make up the largest share of impervious cover in residential developments (about 40 to 50 per cent), a shift to narrower streets can result in a five- to 20-per-cent over-all reduction in impervious area for a typical residential subdivision.

And almost all the pollutants on those streets usually ends up going into the storm drains.

The United States Green Building Council has developed LEED Neighbourhood Development, or LEED ND, which includes not only green aspects of individual buildings, but of their location, as well. Thus, the LEED scorecard takes into consideration such things as how the project or district handles stormwater.

A Canadian version of LEED ND is expected next year sometime, and we might be able to expect a similar concern about stormwater management to be written into it.

Until then, Canadian neighbourhood projects can be registered with the U.S. group, and a couple of dozen have already done that.

Korky Koroluk is an Ottawa-based freelance writer. Send comments to editor@dailycommercialnews.com

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