How do you build an island in Toronto?

David Kusturin stands at the top of a scaffold five metres above the ground just south of Commissioners Street in Toronto’s Port Lands and surveys the busy construction scene before him.

Crews operate massive cranes, augers and concrete pump trucks in a grey landscape vaguely resembling the lunar surface.

Kusturin points to a row of steel beams rising vertically from concrete cylinders buried deep in the ground and explains they will one day form the walls of a 200-metre-wide river valley that will transform this area from a polluted industrial wasteland into an idyllic natural setting.

“We’ll dig a new, kilometre-long river valley and naturalized mouth for the Don River — this creates a new island ringed with parks, where we’ll build the underground utilities, trails, roads and bridges needed to support a future neighbourhood,” said Kusturin, chief project officer for Waterfront Toronto, the agency overseeing the $ 1.25 billion Port Lands Flood Protection Project, one of the largest non-transit infrastructure projects currently underway in North America.

Drill rigs install caissons for cut-off walls that will support the banks of a new river valley being constructed in Toronto's Port Lands neighbourhood.

The new island, named Villiers Island, will feature parklands, walking and biking trails, and residential and commercial real estate (not to mention great views of the city skyline). It will also feature the only natural shoreline within the inner harbour, allowing for easy entry into Lake Ontario with canoes and kayaks.

“The fundamental challenge is to achieve three big goals: flood control, naturalization and placemaking,” said Kusturin, who is responsible for making sure projects undertaken by Waterfront Toronto are properly staffed, procured, and completed on time and on budget.

The Port Lands, located south of Lake Shore Boulevard between Leslie Street in the east and Cherry Street in the west, are a primarily industrial and commercial neighbourhood built on landfill that was once home to oil tank farms, factories and a city incinerator.

In the early 1900s, the Don River’s natural pathway to the lake was essentially cut off and given a hard-right turn into the Keating Channel, which runs east-west to the inner harbour. This design meant flooding of the lower Don was possible during heavy rain storms as water surged towards the small channel to Lake Ontario.

A rendering of Villiers Island being created in Toronto's Port Lands shows the new route the Don River will soon take to Lake Ontario.

In 2007, Waterfront Toronto launched an international design competition seeking ideas about how to naturalize the mouth of the Don River while providing flood protection for the Port Lands, South Riverdale and Leslieville in an extreme weather event. Water normally flows in the Don at a rate of two to four cubic metres per second, but jumps to about 1,560 cubic metres per second during a regulatory storm.

The winning design, by American landscape architectural firm Michael Van Valkenburgh Associates, restores the Don’s more natural approach to the lake and provides three routes for floodwaters to follow if necessary.

“The 90-degree turn at the Keating Channel is not where the river wants to go, so we are helping it along by restoring a sense of what its natural conditions were,” said Herb Sweeney, a landscape architect with Michael Van Valkenburgh Associates.

So how do you build an island? Let’s take a look at what has to be done and the challenges to overcome.

River Valley

First, construction manager EllisDon is overseeing the building of cut-off walls. These walls are steel-reinforced interlocked concrete piles drilled all the way down to bedrock, some as deep as 55 metres, that effectively hold up the banks of the river. They also prevent groundwater, of which there is plenty in the Port Lands, from flowing into the river.

The island will feature parklands, walking and biking trails, and residential and commercial real estate.

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Once the cut-off walls are complete, crews will dig the riverbed starting with an east-west route just south of Commissioners Street. They will then begin digging north to where the Don Roadway meets Lake Shore Boulevard to connect with the existing river where it turns into the Keating Channel. Massive dams, known as “plugs,” will be constructed at either end of the new river to prevent water from the lake and the Don River from flowing into the new river valley before landscaping is completed. It’s expected that 1.3 million cubic metres of earth will be removed during the excavation of the river valley.

“We have this big meander that does a more or less kind of a switchback in the centre of the project,” Sweeney said. “It makes the parks that much more interesting because we’re recreating these natural forms that don’t really typically happen in the city.”

Groundwater

The next step will be to pump the groundwater out of the area in order to build the riverbed, which will be between three and six metres deep when completed. Joey Herrington, senior project manager of soil remediation and earthworks for Waterfront Toronto, said water will be pumped into a pond where crews adjust pH levels, manage sediment and skim petroleum hydrocarbons off the top. The water is then sent to a treatment plant that has been specially built on the site where it will be continuously treated to meet provincial water quality objectives and discharged into the Shipping Channel.

Naturalization

As the groundwater is pumped out, work on the riverbed can begin. This involves constructing a base of stone known as fill aggregate — essentially gravel — one metre thick to act as a drainage layer. A clay liner will rest above this to keep the groundwater from percolating up into the river. At certain locations along the river channel, layers of special soil containing activated carbon will act as filters to prevent any petrochemical contamination that may exist in groundwater from seeping in to the river.

The new island will have great city skyline views.

About a year before any water will begin to flow, however, tens of thousands of plants, including sedges, grasses and rushes, will be planted along the river’s edge.

“In order to prevent the plants from being washed into the inner harbour by the river, they need time to establish root systems,” Kusturin said.

Large rocks called armour stones about two cubic metres in size will be placed in certain areas to ensure the river does not leave its banks when water flows increase in a major storm.

The dam or plug on the lake side will then be removed to allow lake water to gently flow into the river. Finally, at the end of 2023, the plug at the north end of the river valley just south of Lake Shore Boulevard will be removed and the Don River will start flowing along its new route.

“We’re going to make it as smooth as we can because fast-flowing water can be damaging,” Kusturin said. “It will be a very delicate process.”

Ground level

A new river valley alone doesn’t take Villiers Island out of the floodplain. The grade of the entire area will have to be raised an average of two metres to ensure storm water doesn’t breach the banks. This means parts of Commissioners Street, for example, will be raised by about six feet and rebuilt.

Large areas of Villiers Island where new parks and roads are being built are also undergoing soil stabilization. This involves a process known as “surcharging” in which soil excavated to create the new river valley is spread across the land and tamped down. Once the soil has had a chance to settle — between three months to a year — it is removed, leaving the ground beneath compressed and hardened. This ensures the ground won’t sink once work begins on top of it.

Kenyon Wallace

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