May 10, 2012

CITY OF TORONTO

The above proposed “islands” in Humber Bay could improve Sunnyside Beach water quality. The islands would be built from clean fill excavated in future Toronto underground construction projects.

Toronto studies construction of new islands

PETER KENTER

correspondent

How do you dispose of more than two million cubic metres of clean fill while improving water quality, the local environment and recreational opportunities? The City of Toronto is attempting to answer that question with a $3-million study examining the creation of new landforms in both Ashbridges and Humber Bays.

The Waterfront Landforms Environmental Assessment Study will be led by the Toronto and Region Conservation Authority (TRCA) in collaboration with Toronto Water, the Parks, Forestry and Recreation Division, and Waterfront Toronto.

“With a lot of construction happening in the city, we’ve exhausted a lot of local sites for clean fill disposal,” says Lou Di Gironimo, general manager, Toronto Water.

He notes that contractors working on Toronto infrastructure projects are now transporting excavated material further and further outside the city, resulting in increased haulage costs and tipping fees that are adding to construction budgets on city projects.
View Larger Map

Based on current capital program forecasts, Toronto Water will generate an estimated 800,000 cubic metres of clean excavated fill over the next 10 years in constructing both tunnels and underground storage structures. TTC and Metrolinx projects will generate more than 800,000 cubic metres from the Eglinton Crosstown Project alone.

Private construction activity will also create significant quantities of excavated material. The proposed landforms could consume at least two million cubic metres of clean fill.

The Humber Bay landform concept would see the construction of several islands designed to improve the water quality of Sunnyside Beach and provide additional shoreline erosion control.

“Most of the ecological issues are related to what’s coming down the Humber River,” says Di Gironimo. “One of the purposes of the landform would be to improve water quality at the beach by deflecting the flow of the Humber.”

The initial concept, revived from an earlier study conceived about 10 years ago, shows a landform that would begin with the build-up of a solid land mass below the water surface. This would emerge as a series of four interconnected park islands extending an estimated one kilometre south into the lake, east of the Humber.

“The study would determine just how such a landform could be built,” says Di Gironimo.

“Typically, these features look at some sort of protection along the outer edge that begins subsurface, so we need to see if concrete or stone would be used to provide protection from erosion so that fill could be placed within it.”

Di Gironimo notes that clean fill would likely be supplied by barge and dredge.

“From a construction standpoint, it’s a bit of a tough site to access because the area is already an active park,” he says.

The Ashbridges Bay landform concept would be located south of the Ashbridges Bay Wastewater Treatment Plant, and would include a stormwater wetland and a combined sewer overflow high-rate treatment facility, integrated with other projects planned for the area.

“Most of Ashbridges Bay was built by lake-filling, moving southwards from Lake Shore Boulevard in the 1940s,” says Di Gironimo.

“Over time the Ashbridges Bay Wastewater Treatment Plant has taken shape. It still has the ability to go further south within the plant’s existing water lot.”

The concept incorporates a naturalized shoreline and pedestrian path linking Tommy Thompson Park and Ashbridges Bay Park.

“The Martin Goodman Trail currently has to run around the sewage plant,” says Di Gironimo.

“This would bring the trail closer to Ashbridges Bay and could incorporate a pedestrian bridge.”

TRCA will first proceed with an environmental assessment study to determine potential impact on aquatic habitat, navigation, water flows and erosion.

The study would also provide an estimate of reduced costs for haulage and disposal of excavated material for city capital projects.

“We have the authority to issue a proposal call for further studies in 2013,” says Di Gironimo.

“The studies would take a couple of years, followed by a public consultation and approval process.”

Print | Comment