August 24, 2007

Environment

Construction will need to protect lost rivers

Builders need to be prepared to enlist expert aid

SAUL CHERNOS

correspondent

TORONTO

You can bury creeks and streams, but construction crews can’t make them disappear. Stroll along Bloor Street, shop in the Eaton Centre or visit friends in uptown Toronto, and you could be walking on water.

Toronto’s legendary lost rivers criss-cross the city in a seemingly haphazard, meandering fashion. Evident in the city’s widespread ravine system but otherwise hidden beneath concrete, these rivers surface from time to time in conversation, not to mention the occasional flooded basement, cracked foundation and sink hole.

It wasn’t always like this. Hundreds of years ago, southern Ontario was a woodland paradise, dotted with creeks and streams, a remnant of glaciers that carved long, narrow ridges into the landscape. Mostly flowing northwest to southeast, these waterways served as natural carriers for rainfall and melting snow.

“There used to be fish and wildlife in these creeks, and the mouth of the Don River had a beautiful delta,” says Helen Mills, a local conservationist who leads lost rivers walking tours across Toronto.

“You can get a vague idea of what it might have been like by visiting the ravines near Moore Park (Mud Creek) or by going to the mouth of the Rouge River.”

Human activity spelled an end to this natural beauty. The waterways, receptacles for raw sewage and other waste, became increasingly polluted and were integrated into modern-day storm-sewer pipes starting in the late 1800s.

Today, past stewardship practices are coming to the fore.

“In some of the older neighbourhoods of Toronto, and in many of the suburbs that were built in the 50s and 60s, you find many houses with water ‘issues’ in their basements,” Mills says. “Well, map the houses and then map the rivers, and you’ll find a remarkable correlation.”

Not that proximity to a buried waterway heralds disaster, or that they are the only source of trouble. “You can be very close to a creek and have no water issues, and you can be on fairly high ground, on some sort of aquifer, and have problems,” Mills says.

"The onus is on the builder to build according to the situation he finds himself in."

Ted Bowering

City of Toronto

Ultimately, she explains, water goes where it wants. Even when an old creek is embedded within a sewer system, water often continues to flow outside the pipe.

Builders can help protect their projects and the environment by avoiding development where the water table is high and by retaining stormwater on-site for use in toilets and urinals and for watering gardens, Mills says.

Ted Bowering, policy and program development manager with the City of Toronto’s water department, says builders need to be sensitive about where they’re working and retain engineering help to identify any underground water activity.

“The onus is on the builder to build according to the situation he finds himself in,” Bowering says.

Where a water table is high, work crews can de-water an excavation site using wells and pumps or other techniques. Builders require permits if they need to channel any groundwater into sanitary or storm sewers.

Storm sewers go straight to the river or lake untreated, so builders must treat the water themselves in accordance with city criteria. The city also wants to avoid large quantities of groundwater entering sanitary sewers; thus, the city regulates the use of all sewer systems through permits and fees.

Bowering says the city wants to reduce the number of connections to storm sewers from building sites, so it is asking builders to consider alternative measures, such as increasing foundation strength and impermeability.

“If you build a building in a creek or water table, you should be prepared to keep that basement waterproof,” Bowering says. “Otherwise you’re just asking for trouble.”

Cracking and sink holes can also occur where water tables are high, and contaminated groundwater can turn an otherwise normal-looking site into a brownfield, requiring special treatment.

“It’s really the geotechnical and hydrogeological engineers who would be aware of issues, like these, that you need to look out for.”

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