Urban design in the age of climate change: befriending floods

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How to design a flood-prone city? You don’t. How do you prepare for extreme weather in the age of climate change? You let the water come.

This is the approach that landscape architects and other designers are taking to deal with the threat of flooding in urban areas: designing urban landscapes designed to absorb water; and the edges of rivers and lakes that are intended to be wet.

The funding announcement last week in Toronto for the Port Lands Flood Protection Project, to which Prime Minister Justin Trudeau and his counterparts in Ontario and Toronto have committed nearly $1.2 billion, reflects a big bet on this model.

This project, based on a design led by landscape architects Michael Van Valkenburgh Associates and urban designer Ken Greenberg, is not based on heroic engineering. It reshapes the mouth of the Don River in downtown Toronto; where the river once meandered through a swamp on the edge of Lake Ontario, it has been shaped into a concrete channel for more than a century. The new project will reverse some of these changes. “Rather than building tall dikes,” says Greenberg, “it creates a large expanse of parkland that would be flooded in the event of severe events – but would also create a new neighborhood.”

The ‘Don Mouth Naturalization Project’ plan includes a large new park and estuary in the Don lowlands.

Toronto waterfront image

The Don River flows south to Lake Ontario, but makes a last-minute right turn into the concrete-lined Keating Channel. The new design will keep that in place but add a second exit, this one wide and bordered by a bowl-shaped park. This green space will be the heart of new neighborhoods, home to tens of thousands of people, which can only be built because the risk of flooding has been reduced.

The adjacent Ile de Villiers, a 54-acre piece of town, is already being planned. It is an urban planning and landscape architecture project, linked to flood protection and adaptation to climate change – the effects of which are already manifesting themselves in more frequent floods like those of the river of the Outaouais this year. “It’s a problem that requires lateral thinking, breaking out of individual silos,” says Greenberg.

It also requires a new conceptual approach to the problem: “Letting the river shape the city, rather than the city subverting the river,” says Nina-Marie Lister, a planner and ecologist at Ryerson University. The planning for Corktown Common, a nearby park in Toronto that also offers flood protection, is a good example of such flexible thinking, says Lister, who is also a member of the Ryerson Urban Water Centre. It’s “a smarter way to design,” she says. “But we’re just not very good at it, institutionally.”

The slide and sand playground at Corktown Common Park in Toronto.

Deborah Baic/The Globe and Mail

Why? Lister speaks of rivers as “living systems,” and governments, civil engineers, and city planners don’t treat living systems well.

“We tend to use machine metaphors, and river systems don’t work that way,” Lister says.

The challenge is to create urban spaces that “prepare for routine but inconsistent flooding,” she says. “We know it’s going to happen, but it’s unpredictable. The planners don’t like that idea. It scares us.”

In the Netherlands, a series of 39 projects dubbed “Room for the River” allows for such uncertainty, creating canals and diversions that direct flooding away from vulnerable areas. And while Lister points out that these rivers — indeed a large part of the Dutch landscape — are heavily planned and managed, she says, “there are huge lessons for Canadian cities. … How do you design something that you do not want?”

Smaller landscape interventions, in large numbers, can help by diverting stormwater away from storm sewers and river systems. Key tools include swales – small gardens that capture and absorb rainwater – and green roofs. “For stormwater, green roofs are an amazing solution, because you have all that unused roof space,” says Liat Margolis, professor of landscape architecture and director of the Green Roof Innovation Testing (GRIT) Laboratory at the University of Toronto.

The Green Roof Innovation testing lab includes several different flowerbeds.

PHOTO COURTESY OF DANIELS FACULTY

Indeed, green roofs are proven to absorb a substantial amount of rainwater. And a cistern, or holding tank, can keep it out of storm drains and off the ground; Margolis and GRIT Lab are studying the combination of the two systems. Rainwater will be used to irrigate the green roofs, and the green roofs absorb some of the pollutants in the water. “We know that green roofs are very effective in reducing flooding,” says Margolis. “Can we maximize that and also clean up the water along the way?”

Toronto’s chief city planner, Jennifer Keesmaat, cites the city’s pioneering 2010 green roof policy as an important ingredient in reducing the quantity and quality of rainwater. She also cites Raindrop Plaza Park, a new small park designed to deal with flooding in a specific area of ​​the city by absorbing rainwater.

But Don River’s move, she says, reflects a larger lesson. “It’s about mitigating the mistakes of the past,” says Keesmaat. “It was the unnatural diversion of the Don that caused this threat. We now have to spend $1 billion to get it right because there was a planning philosophy that we can control the water, and it turns out turns out we can’t.”

The new plan for the mouth of the Don River “creates a large expanse of parkland that would be flooded in the event of severe events – but would also create a new neighborhood,” says urban designer Ken Greenberg.

Toronto waterfront image

So if we can’t control flooding, should we stay away from it? It’s an eternal debate whenever an urban area is hit by flooding: does it make sense to start building in a floodplain? More than 1.8 million Canadian households live in floodplains. This spring’s flooding in Quebec has resulted in calls for disaster relief and little change in planning, just as Calgary’s major flood in 2013 led to the reconstruction of many damaged buildings in the floodplains and no major change in the city’s land use planning policy. Frank Frigo, senior planning engineer with the Calgary Water Utilities Department, says the city carefully monitors flood risk for new suburban developments.

“The challenge for us is the existing city,” he says, especially the core. “Due to a historic accident, our most intense development and infrastructure is at risk.” Calgary has carefully considered a “room for the river” approach, but the costs of abandoning land in the floodplains would simply be too high.

Alec Hay, a civil engineer and expert in resilience – a community’s ability to survive and bounce back after a disaster – says the response, of relying on controlling water levels, won’t always be adequate.

Corktown Common Park is a good example of flexible development that allows ‘the river to shape the city, rather than the city’. [subverting] the river,” says Nina-Marie Lister, a planner and ecologist at Ryerson University.

Deborah Baic/The Globe and Mail

“The biggest thing people can do is pay attention to where they live,” he says. “If you live in a flood-prone area, don’t be surprised if you flood.”

Working with Calgary residents after the 2013 disaster, Hay found that “there were people who would honestly say, ‘This won’t happen again.’ … And, of course, it will.”

Designing a new part of town to be flood proof is one thing; fortifying or even abandoning existing riverside neighborhoods is, politically, quite another thing. But if the rivers are living beings and we live alongside them, we must be prepared for them to rage.

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