Silva Cells Part of the Massive Six Points Interchange Retrofit in Toronto – Case Study

Silva Cells helping Toronto meet their Green Standard Goals

Silva Cells are managing 55% of the stormwater catchment area in this 6.47-hectare site

Over 300 street trees, each one planted with an average of 30m3 of soil

46% annual runoff removed

74% total phosphorus removed

83% annual (TSS) total suspended solids removed

2,756 m³ of available stormwater storage volume

The Etobicoke Six Points Interchange, locally known as “Spaghetti Junction”, is getting an extreme makeover. A key feature of the makeover in the Toronto, Ontario suburb is the addition of over 300 street trees, each one planted with an average of 30m3 of soil. DeepRoot Silva Cells provide 80% of the soil volume under the sidewalks and plaza areas, providing loosely compacted soil to help grow great urban trees while managing over 55% of the stormwater catchment area throughout the site. Other features are the removal of 3 bridges, and the addition of new roads that are pedestrian and cycling friendly with separated bike lanes.

Silva Cells are managing 55% of the stormwater catchment area in this 6.47-hectare site

The interchange reconstruction comes at a cost of $50 million dollars (CAD/$36M USD) and 5 years of construction. The planning, engineering and design has been in the works for over twelve years, and anticipated for decades. The project team included three designers (HDR, SvN, & WSP), a General Contractor, (Fermar) and the client, City of Toronto. The Landscape sub-contractor that installed the Silva Cells was CRCE.

The 2 Phase project expands throughout the pulsating, Etobicoke Center at the “Junction” of Kipling, Dundas, and Bloor St.

Map of Six Points Plaza and surrounding boroughs, and airport. The Six Points Intersection Construction project is near the Six Points Plaza. Image courtesy of google maps

Challenges in the planning included meeting the demands of a growing population and a thriving economy, while incorporating green infrastructure in the new development. The existing interchange was a known disaster that would take immense planning and funding to fix. This was achieved through teamwork and cooperation. Fermar, the General Contractor wrote,

“The removal of three existing bridges including the reconstruction and realignment of various roads and the new road construction of three new roads, were all included under the contract making this project a complex one to navigate. It took the team time to prepare a comprehensive schedule on how the work could be carried out without substantially interfering with the high vehicle and pedestrian traffic and while keeping the community and the workers safe.”

The city of Toronto took the opportunity to meet the needs of commuters, drivers, truck haulers, but also the local community of pedestrians and cyclists. There were also some serious environmental challenges to meet at the local and municipal level.

Timeline: The Evolution And Phases Of Six Points

The City of Toronto has long been concerned with effectively managing population growth. Toronto is now the 4th largest city in North America, behind Mexico City, New York and Los Angeles. In 2008 Toronto underwent a Municipal Class Environmental Assessment (EA) to examine options to reconfigure the Six Points Interchange, supporting the development of the Etobicoke Center. Between 2009 and 2011 the city went through an urban design study which included detailed streetscape designs for new roads, pedestrian clear zones, market zones, and tree planting zones. The idea to transform the outdated intersection has been around for decades. In a 2018 Globe and Mail article about the project, The Senior vice-president of development at Build Toronto (the project lead) stated, ”We are envisioning a community that will be highly connected with the Kipling subway with great pedestrian pathways and interconnections, parks, residential with some retail and office uses.”

Phase 1 ran for two years from 2015-2017 and included the demolition of three existing bridges and roadways. Phase 2 started in March of 2017 and is scheduled to be finished in the next few months.

The Toronto Green Standard

Toronto is a leader when it comes to setting and achieving green infrastructure goals for the city. A primary requirement for the Six Points Interchange was to comply with the Toronto Green Standard which is Toronto’s sustainable design requirements for new private and city-owned developments.

The Standard addresses the City of Toronto’s environmental priorities including improving air quality, reducing the urban heat island effect, and reducing stormwater runoff while improving the quality of stormwater draining to Lake Ontario. With the goals and the environmental standards bar set high, DeepRoot’s Silva Cells were able to provide solutions to help achieve the Green Standard Goals.

“The use of Silva Cells as part of the quantity control infrastructure for Six Points, significantly reduced the funds needed for installation of additional single purpose quantity control grey infrastructure.”
Patrick Cheung, P.Eng. Senior Engineer, Toronto Water

Phase 2, 2019. Silva Cells are under the new paths, joining up the planters with a continuous soil volume, in a parklet near the interchange. Image courtesy of CRCE.

Six Points Interchange received a 2018 RAIC National Urban Design Award of Merit as well as a 2017 City of Toronto Urban Design Award of Merit

Soil Volume Requirement and Canopy Targets:

To achieve the goal of 40% tree canopy targets, the city requires that each street tree be planted in a minimum of 30m3 of soil. These large volumes of uncompacted, water absorbent, aerated planting soils help to ensure that the trees will grow to maturity and provide significant canopy in an otherwise concrete heat island.

Stormwater Mitigation:

The large volumes of uncompacted soils in the Silva Cells also act like a giant underground bioretention swale. More than 55% of the surface runoff (3.56 hectares) from the site is directed from street and sidewalk catch basins into the Silva Cells where the water is distributed into the soil through a network of perforated pipes.

Silva Cells helped to exceed project stormwater design goals:
46% annual runoff removed
74% total phosphorus removed
83% annual (TSS) total suspended solids removed
2,756 m³ of available stormwater storage volume

The dual use of Silva Cell as both a tree and stormwater tool meant the Silva Cell could provide stormwater services as a source control that provides quantifiable retention, detention, and water quality benefits at minimal additional cost. The soil was already paid for by using the Silva Cell to meet the mandatory soil volume standards, providing the stormwater benefits at substantially lower cost than could otherwise be managed.

Non-perforated pipes distribute water from catch basins through the Silva Cells and provide temporary storage, like a swale in a bioretention swale. Black perforated pipes drop water around the tree root-ball and every 2 meters down the sidewalk throughout the Silva Cells.

Project Water Flow Diagram: Street and Sidewalk water flow from the Catch basins to Silva Cells. Showing where the water slowly perks through the loosely compacted soils. Retention, detention and water quality criteria are met by the soil in the Silva Cells in addition to watering the trees. An aggregate cistern below the Silva Cells provides additional Detention and a 300mm overflow subdrain takes excess water back to the Main Storm line.

“By integrating the roadway drainage component of the Six Points reconfiguration into the Silva Cell system, the stormwater management objectives of both municipal and provincial regulators were successfully achieved with minimal footprint area, including runoff attenuation, pollutant removal and water balance criteria”
-Anthony Reitmeier, Senior Project Manager, HDR Corporation.

2X Silva Cell installation in 2018. Stormwater Distribution pipes in the Silva Cells and washed rock cistern with a 300mm overflow Drain line at the bottom.

The Trees

300 diverse, healthy street trees, a total of 13 different types
Botanical name and Common name:

Acer X Freemanii Freeman Maple
Acer Rubrum Red Maple
Acer Saccharinum Silver Maple
Celtis Occidentalis Common Hackberry
Ginko Biloba Ginkgo
Greditsia Triacanthos Green Honey Locust
Liriodendon Tulipfera Tulip Tree
Platanus X Acerifolia Exclamation Plane Tree
QUercus Rubra Red Oak
Tilia Americana Redmond Basswood
Ilmus Americana American Elm ‘Princeton’
Ulmus Americana American Elm ‘Valley Forge’
Zelkova Serrata ‘Japanese Elm’

Road B lined with dozens of Maple Trees. Photo taken 2018

Map of Six Points interchange, birds eye view. Gray shaded areas are the stormwater catchment area.

Installation Summary

4,994 2x and 5,718 3x Silva Cells.
30³ of soil volume per tree, totaling 9190 m³ soil.
2,756 m³ of available stormwater storage volume
Integrated Trees and Stormwater
Municipal/Government Project: City of Toronto
Project Designer: HDR, SvN, and WSP
Contractor: Fermar and CRCE
Installation Date: 2018 – 2020

If you have any questions about this project or this case study please contact Mike James at [email protected] or Kala Hunter at [email protected]

Silva Cell and perforated water distribution pipes, view between dozens of posts, taken 2018.

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