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‘Burying rivers is not a great idea:’ Cities work to uncover their hidden waterways

Cities around the world are opting to bring rivers back to light.

Burying rivers underground used to be common in urban planning, but centuries of man-versus-nature reshaping of the landscape is now being rethought.

While many new developments are being designed to work within natural landscapes, existing cities — built atop networks of culverts and sewers where creeks and rivers used to flow — are looking for ways to bring forgotten waterways back to the surface.

“I think that people recognize now that burying rivers is not a great idea,” says Claire Oswald, a watershed hydrologist at Ryerson University.

Aside from ecological and aesthetic reasons for maintaining above-ground waterways, there are also practical issues at play. Pipes can only hold so much water before overflowing or bursting, while rivers with porous banks can offer increased stormwater capacity as climate change alters precipitation patterns.

A stretch of the Sawmill River disappears into a culvert in Darmouth, N.S. (Jill English/CBC)

But reversing a wrong and “daylighting” rivers, as the practice is known, isn’t easy.

“In some places, it’s just going to be impossible,” says Oswald. “You’d have to rip out people’s homes and streets, and things like that, to be able to bring a waterway back to its natural course.”

Still, where it is possible, daylighting is gaining traction with urban planners, with success stories popping up in cities all over the world — from Auckland to Seoul and London to Zurich, as well as communities in Canada.

“How we think about stormwater has changed so dramatically,” says Halifax city councillor Sam Austin, a former urban planner. “Now it’s about slowing it down, managing it on the landscape as best you can.”

Halifax city councillor Sam Austin, a former urban planner, says the thinking about managing waterways and runoff has ‘changed so dramatically.’ (Jill English/CBC)

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Daylighting the Sawmill River

A project under way in the Dartmouth Centre district is a local daylighting success story.

The Sawmill River used to run naturally through Dartmouth’s downtown. It was banished to an underground pipe after major flooding in the 1970s, a result of heavy rainfall from Hurricane Beth and a collapsed dam.

Hurricane Beth caused significant flooding in Dartmouth, Nova Scotia’s downtown in 1971. The city responded by channeling the Sawmill River into a buried culvert to manage stormwater. 0:47

Half a century later, the 2.5-metre culvert was due for replacement, and a rethink.

“[With] all the development in the drainage basin, climate change, all the projections were the pipe is not going to handle a repeat Hurricane Beth event,” Austin says. “So doing this, it was actually a have-to project.”

This video from The National takes an in-depth look at the Sawmill River project, and some of the challenges of daylighting a waterway:

Unearthing the buried Sawmill River in Nova Scotia via ‘daylighting’ is a lengthy process but comes with environmental and economic benefits. The Fix looks at why the river was buried in the first place and the challenges presented by the process of ‘daylighting.’ 7:09

Fortunately for the city, federal infrastructure money came down the pipe at the same time that the city was pondering how to fix the problematic culvert. But it was tied to the condition that the city restore fish passage from Halifax Harbour into Dartmouth’s chain of lakes — an ecosystem that was disrupted when the dark and steady-flowing pipe replaced the natural river.

Other options on the table included installing a wider pipe in addition to building a fish ladder, but daylighting the river solved both challenges and was determined to be the most cost-effective option. The initial phase is complete, daylighting the first 330 metres of the river. Even so, the project is not cheap — phase one cost $ 8.9 million, and no cost projection is finalized yet for phase two.

Phase one of the Sawmill River ‘daylighting’ project has exposed sections of the waterway that used to be piped underground. (Jill English/CBC)

“There are very few times that you have things really line up the way they did for this,” says Austin. “We need to do stormwater. The pipe needs to be replaced. We’ve got federal money.”

And they have the community’s support.

“It’s always easier to replicate the status quo than doing something different like this,” says Austin. “I believe the community support was integral to the solution we ended up with.”

Connecting with the landscape

Toronto resident Helen Mills has spent more than 20 years engaging her community along the routes of buried and destroyed waterways.

Her group, Lost Rivers, serves to both research and teach about Toronto’s many underground rivers, and she says most people care once they know the rivers are there.

Part of phase one of the Sawmill River daylighting project includes fish ladders that help them navigate the waterway to reach lakes upriver. (Jill English/CBC)

“One of the things I’ve learned more and more deeply over the years,” she says, “is the deep way we connect with these rivers through celebrating and understanding that they were there.”

Having built a map of Toronto’s lost rivers and spent years discovering what’s left of them, Mills is familiar with the complicated history between water and urbanization.

“It’s a constant struggle to balance development and the protection of the rivers, and protection against flooding,” she says.

Green infrastructure needed

Ryerson’s Oswald says there are lots of ways to improve on the existing infrastructure.

“[Daylighting] would be part of a large puzzle of strategies we can undertake,” she says.

Halifax councillor Sam Austin surveys the fish ladders on an upstream section of the Sawmill River. (Jill English/CBC)

Other solutions attracting interest include permeable pavement, green roofs, and constructed wetlands, all designed to absorb and retain excess water on the landscape at times of heavy rainfall, slowing water down to prevent flash flooding.

“I think sewers are always going to be part of the solution for managing water in urban areas,” says Oswald, “but green infrastructure is really sort of the future.”

Mills agrees.

“The thinking has changed a lot,” she says. “It’s well-documented and well-understood that green infrastructure is essential.”



CBC | Technology News