They lurk beneath our neighbourhoods, buried in the name of urbanization. But every now and then, they make their presence known when a heavy rainfall brings them to the surface – flooding parks, streets and basements – like a ghost haunting its former abode.
Toronto's hidden creeks and rivers spend most of their lives underground, in the intricate network of pipes and concrete channels that were designed to control these natural waterways. But as last week's severe storm showed, the city's aging water infrastructure is struggling to manage the volume of rain surging through its veins.
Michael Cook, a graduate student in landscape architecture at the University of Toronto who has been exploring sewer systems around the GTA for the past decade, is championing an idea to ease the strain on the storm sewer system: prevent rain from entering the sewers in the first place. One way to do this, he says, is to restore buried rivers and creeks, a practice known as "daylighting" that is gaining traction in cities around the world.
"People want the experience of living with water. We just need to figure out ways to make that possible, make that safe and to make sure the water falling on our cities is clean and doesn't end up flooding our infrastructure," says Mr. Cook, who writes extensively about stormwater management on his website, vanishingpoint.ca , where he also posts detailed histories of the city's hidden waterways, along with photos he takes during his subterranean trips that capture the eerie beauty of Toronto's vast sewer system.
One of the most high-profile examples of daylighting is in Seoul, South Korea, where the city spent $384-million to revive 5.8 kilometres of the Cheonggyecheon stream that runs through the centre of the nation's capital. The process involved ripping up a road and elevated highway that were built on top of the river decades ago. Today, eight years after the river was restored, the Cheonggyecheon has become a green corridor. With air and noise pollution drastically cut, a larger variety of birds, insects and fish have returned to the area; the recovered stream has also become a gathering spot for locals, attracting pedestrians who amble along the grassy banks.
In the late 1800s, concerns about public health prompted the city of Toronto to cover up creeks, which were being used as receptacles for trash and human waste. While it solved one problem, it also created some of the water management issues the city faces today.
The city's long-term wet weather plan includes initiatives to strengthen streams that are already above ground, reflecting the integral role natural waterways play in maintaining Toronto's storm system, "something that is becoming increasingly important with extreme weather events," Michael D'Andrea, the city's director of water infrastructure management, wrote in an e-mail. But, he added, daylighting a buried creek is a much more complicated task given that many of the city's hidden watercourses flow under roads, developed lands or private property.
While daylighting a river on the scale of the Cheonggyecheon stream is unlikely in Toronto, the city has yet to acknowledge the need to hold stormwater in Toronto's upland neighbourhoods, areas that are not usually associated with the kind of flooding seen in the river valleys, says Mr. Cook, who regularly lectures and makes presentations on issues related to sewers, watersheds and buried creeks.
"We need an understanding of how the whole watershed functions" – from where the rain falls to its destination in the lake, he says. "Every step along there, we need to be managing the problem, figuring out ways to store [stormwater] temporarily and treat it, so we're not trying to deal with all these problems at the bottom end of the pipe."
So if the city is serious about diverting rainwater from the sewer system, Mr. Cook says, it should go upstream to Toronto's post-war suburbs, where creeks were often covered simply to make planning and selling subdivisions easier. In some cases, nothing was built on top of buried waterways, so there are empty stretches of grass that are ideal starting points for daylighting, he says.
He has identified at least eight waterways in the GTA, which run either partly or completely under open spaces, that he says could be revived today. Wilket Creek, for example, flows through a drainage pipe that travels under several North York neighbourhoods, like Willowdale, before emerging as an above-ground stream and then dipping down to the Don River. While the upstream portion of the creek near Yonge and Finch is heavily developed, the waterway's path south of Sheppard Avenue flows almost entirely under empty grassland.
When rain falls on a natural watershed, it slowly percolates through the soil and plants – which act as a natural filter, stripping away some of the pollutants that stormwater picks up as it trickles off sidewalks and roadways – and then collects in a creek or river. But with storm sewer systems, all that water is concentrated in large volumes underground, where it rushes through the pipes until it's released into the lake. During heavy rains, the sewers quickly become overwhelmed.
"So the kind of flooding we experienced on the Don River – just [last] week and earlier this year – is exaggerated by all these storm sewer systems," Mr. Cook says. "If we had more surface features, like wetlands or daylit creeks, it would take a lot longer for this water to reach the river. And you wouldn't have the same flooding on the DVP or GO train line."
This type of flood prevention was one of the main ideas behind a 1994 daylighting proposal, created by local architects Kim Storey and James Brown, to restore Garrison Creek as a series of connected surface ponds that would collect and filter storm water, which could then be reused for irrigation instead of ending up in the heavily burdened sewage trunk in the Beaches.
While the plan had strong support from local residents, it never came to fruition. "I think it lacked political will," says Ms. Storey, who is an an urban designer and partner at Brown and Storey Architects. "At the time, it was a significant change in the way we thought about treating water in the city."
Now, almost 20 years later, recent events have revived some interest in the plan, she says. In the wake of the storm, residents were tweeting about the Garrison proposal, which can still viewed on the firm's website. A recent documentary, Lost Rivers, which includes a segment on Garrison Creek, has also sparked conversations about the role natural streams play in the progression of cities. Perhaps the renewed interest will provide the push needed to bring Toronto's largest buried waterway back to life, Ms. Storey says. "I think its time has come. Who thought we would have a rainfall like Hurricane Hazel in one evening? That level of weather is not ancient history. It's something that's happening now."