Green infra’s impact on flooding underrated

Expert says cities need hybrid of grey and green infrastructure to reduce urban flooding
Thursday, June 9, 2016
By Rebecca Melnyk

More performance data on the benefits of green stormwater infrastructure (GSI) in extreme weather events is needed as GSI may be more effective than believed, according to Clifford Maynes, executive director of Green Communities Canada, a national non-profit that works with businesses, homeowners, governments and communities to reduce impact on the environment.

Maynes spoke about urban flooding solutions and challenges at the Grey to Green Conference at Ryerson University in Toronto on June 3. Research shows GSI, also known as low impact development (LID), can eliminate run-off from the 90th percentile of rainfall events through managing rain where it falls using functions like infiltration, evapotranspiration and reuse. However, Maynes, along with other experts, said GSI may actually be more efficient at moderating risk for events beyond the 90th percentile.

Take for instance Elm Drive in Mississauga, Ontario that underwent a road retrofit comprised of six bioretention planters and permeable pavement that treats and infiltrates road runoff on an adjacent school property. Ongoing performance assessment has found that LID practices are exceeding all design expectations, providing 99 per cent total suspended solids removal and reducing peak flows for 2-year events by 70-100 per cent.

Such knowledge is helpful in spurring investments and policy changes to solve urban flooding and clear up misconceptions about how GSI complements traditional grey concrete, steel and asphalt infrastructure.

“Catastrophic floods are one of the few instances where people think very deeply about stormwater, the terrible damage it can inflict and the need to do something about it,” said Maynes. “Complex problems equal complex solutions; there’s no easy technical fix and no one organization can easily solve it; it requires solutions across the landscape.”

Research already shows the myriad benefits of green infrastructure: better water quality, erosion control, improved livability of communities and energy cost savings, to name a few.

A report from the Green Infrastructure Ontario Coalition, for which Maynes is chair, points to a number of studies. For instance, The Centre for Clean Air shows green roofs lead to a 15 to 45 per cent savings in annual energy consumption due to lower cooling costs.

Another study from the Environmental Protection Agency Study examined the Laurel Springs residential subdivision in Jackson, Wisconsin. The community was developed with preserved open spaces and bioretention and vegetated swales, resulting in a cost savings of $504,000 (US), or 30 per cent of traditional construction costs.

Yet, while much is known, industry still needs to explore GSI’s contribution to flood control, its peaks and volumes and how it is used in conveyance. Such knowledge will help support the case for GSI so more support will be offered to municipalities whose financial resources remain parched.

Green prospects

There is a progressive rise in unpredictable weather, climate change and impervious pavement, which restricts water from soaking into the ground.

“Infrastructure was also not properly designed during a time when people weren’t thinking about flood management, systems; they weren’t anticipating the degree of intensification that was going to happen,” added Maynes. “Municipalities don’t have the money to keep up with it.”

But the outlook isn’t all together gloomy. Green Communities Canada has seen the federal and provincial government starting to engage with real commitments to green infrastructure policy. Still, the $125 billion infrastructure investment in the 2016 federal budget targeted for the next ten years (Ontario has committed $130 billion) has yet to fully envision how longer-lasting solutions can be created when both green and grey infrastructure work together.

And these solutions are becoming more and more pertinent. A source from the Toronto Region Conservation Authority notes that 95 per cent of run-offs the organization addresses is attributed to urban flooding—not rivers, a statistic that Maynes said probably doesn’t cover all the damages.

“There is lot of damage due to urban flooding that gets reported publicly,” he noted. “But there’s a lot that doesn’t get reported because it’s uninsured damage, or if you are insured, you’re worried that too many claims will get your coverage withdrawn or property values will go down if the neighbourhood appears to be vulnerable to floods.”

Going forward, Green Communities Canada is now a part of a provincial Urban Flooding Collaborative that seeks solutions to urban flooding by developing a shared knowledge base and finding a range of committed stakeholders.

In addition to rallying for policy change, its member organization, Rain Community Solutions, has developed a “Soak it Up! Toolkit” for property owners and municipalities with how-to information for managing rainwater on land to reduce risk and save money, while protecting waterways and communities.

“There is going to be flooding; we’re not going to eliminate it,” said Maynes, who witnessed the great flood of 2004 in Peterborough, Ontario that saw 150 mm of rain in parts of the city in less than an hour. “So, how are we going to maximize green infrastructure in managing that?”


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