June 28, 2012

CITY OF TORONTO

Humber Creek in 1997 before undergoing daylighting.

FEATURE | Sewer and Watermain/Water & Wastewater

Reviving Toronto’s natural waterways

PETER KENTER

correspondent

Toronto is marked by dozens of streams and waterways that have long since been filled in or channeled underground through pipelines. In some cities, the process of daylighting—reviving natural waterways—has become a popular cause. For local supporters of the idea, much of the emphasis is on two waterways, Taddle Creek and Garrison Creek, both of which wend their ways from mid-city to Lake Ontario.

While the city is committed to naturalizing and improving existing open waterways as part of its overall water infrastructure program, the likelihood of daylighting any buried waterways in the near future is minimal, says Michael D’Andrea, director of Water Infrastructure Management with the City of Toronto.

“The typical approach and standard practice in the past, right up to the 1950s and ‘60s, has been to fill in creeks and waterways or channel them underground to allow urbanization and development to occur,” he says. “If we want to unearth river systems that are in pipes, there are a number of challenges in terms of where we could effectively daylight those waterways.”

Those challenges include waterways running across private property, major developments and roadways and even under cemeteries.

“If you were to daylight just for the sake of daylighting, you’d need more property than some people believe to re-establish a natural system,” he says. “Even in those locations where the waterway could be surfaced, the cost would be significant and you may no longer have the extent of the land

CITY OF TORONTO

Humber Creek in 2002 after undergoing daylighting. where you could truly naturalize the waterway with side slopes and flood plains and room for a naturalized habitat.”

Naturalized waterways are also far from static. As water flows through them, they erode and meander, a process that may have significant impact on infrastructure in an urbanized setting. Flooding and peak flows may also cause significant erosion scars.

The city is, however, actively naturalizing and restoring streams and waterways that remain above ground as part of its wet weather flow master plan. That plan, established in 2003, recognizes that natural waterways form a significant part of the integral functioning of the city’s storm drainage system.

“The concrete-lined channels that were built in the 50s and 60s were designed to move large volumes of storm flow without consideration for monitoring aquatic habitat,” says D’Andrea.

“These channels are deteriorating. We are now applying stream naturalization techniques, using bioengineering technologies to strengthen banks, using plantings of different sorts and re-engineering stream bed design, which stabilizes the stream channel. These new designs can provide aquatic habitat features while also handling large flows.”

Engineered solutions include the use of armourstone walls, instead of rock-filled wire cages, to shore up shorelines and the addition of large rocks, stilling basins, deeper pools and other structures to help slow rapid flows. Success stories include the naturalization of Humber Creek.

“Toronto is considered a leader in stream naturalization,” says D’Andrea. “Stream restoration contractors who specialize in this sort of work will be looking at a growth industry in Ontario.”

James Brown, a principal with Toronto architecture firm Brown and Storey, however, believes that even if a daylighted stream can’t be thoroughly naturalized, some portions of existing waterways can be resurrected as a series of interconnected ponds. The firm has completed daylighting design plans for both Garrison and Taddle Creeks.

“If you simply disconnected the storm lines in certain areas and allowed the water to be stored in ponds in parks and open areas, you could take a load off the system and minimize the need for storm water treatment,” says Brown. “If too much water collected in those ponds, you could simply allow the overflow to return to the storm water system.”

It would be an incremental approach that would take advantage of public lands, such as parks and schoolyards. The ravine carved out by the Taddle Creek, for example, still defines the city’s Philosopher’s Walk, behind the Royal Ontario Museum.

“You can see the pipe infrastructure that carries the creek water just below the surface,” says Brown. “That would be an ideal location to begin the process.”

Such a concept is on display at Toronto’s Sherbourne Common waterfront park, featuring an urban stream and a series of interconnected water detention ponds.

“While the idea is appealing, I really do dislike the term ‘storm water detention,’” confesses Brown. “It’s like you’re putting water in jail.”

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