Stormwater Management in the Median Silva Cell Case Study

Central Parkway is a low impact development (LID) retrofit streetscape project in Mississauga, Ontario. The project utilizes Silva Cells as an underground bioretention system to manage and treat stormwater runoff while simultaneously providing the uncompacted soil volume necessary to grow large trees. At Central Boulevard, the City of Mississauga...

Central Parkway is a low impact development (LID) retrofit streetscape project in Mississauga, Ontario. The project utilizes Silva Cells as an underground bioretention system to manage and treat stormwater runoff while simultaneously providing the uncompacted soil volume necessary to grow large trees.

At Central Boulevard, the City of Mississauga partnered with DeepRoot, TD Friends of the Environment Foundation, and Credit Valley Conservation to install the Silva Cell system as well as performance assessment equipment in order to monitor site performance, focusing on water quality as well as quantity.

Stormwater has become an increasingly important issue to the Greater Toronto area over the past several years as the population has quickly increased at the same time that the area has begun to experience more frequent, high intensity storms due to climate change. Polluted runoff from these events flows from hardscapes and enters into the Great Lakes, negatively affecting water quality, causing erosion, and harming the local ecosystem.

The median prior to installing Silva Cells

Silva Cell installation underway

Trees were planted, and stormwater monitoring began, in 2015

The Silva Cell system at Central Parkway acts as an underground bioretention system to remove stormwater pollutants and to control runoff volume for water flowing into Cooksville Creek and Lake Ontario. Runoff from 1,046m2 of surrounding impervious surfaces is directed into existing catch basins and then throughout the system via two distribution pipes. The soil acts as a filter to remove nutrients and excess water is discharge to a storm sewer through an underdrain at the base of the system.

Performance findings from 2015 show very strong preliminary performance with a 97% average stormwater volume reduction and a 96% peak flow reduction as well as helping to replicate a natural water balance in an urban setting, contributing to erosion control, improved water quality, and protection of natural aquatic habitat.

The integrated approach also allows for aesthetic value by way of six salt-resistant Chanticleer pear trees that are planted in the median to provide green canopy cover along the roadway. The trees have access to 233.33 ft3 of soil each and the Silva Cells plus planter area for the project provide a total soil media volume of 105m3.

You can read an initial report of the study on the Credit Valley Conservation website.

Installation Summary
Average soil volume per tree: 233.33 ft3 (6.61 m3)
Number of Trees: 6
Total Silva Cells: 140 Frames, 70 Decks
Installation Date: 2015
Intallation Type: Integrated—Trees and Stormwater
Project Site: Municipal/government
Project Designer: City of Mississauga
Contractors: Pacific Paving Inc.

 

Top image: Credit Valley Conservation

Source: www.deeproot.com