92 Trees Enhance Downtown Banff, Alberta: A Silva Cell Case Study

– In 2021, a near 30-year-old vision to create a cohesive, connected, and safe thoroughfare came true for both Bear and Moose streets in Banff, Alberta.
– Embodying the natural beauty of cascading mountains and the National Park surrounding the town, designers WSP and The Tula Project incorporated 92 street trees along the redesigned Bear St.
-Prioritizing public safety while updating outdated underground utilities and adding Silva Cell infrastructure is a triple win for Banff’s public space.

Bear Street Looking North – Downtown Enhancement Concept Plan from 1992

Banff is Canada’s oldest National Park, and today sees anywhere from 3 to 4 million visitors a year. The Town of Banff sits within the park, and with only 8,000 residents caters mainly to the millions of visitors and tourists with its inviting restaurants and shops along Banff St. and Bear St., its main thoroughfares. Today, thanks to the renovations, Bear St. is an even more inviting streetscape that maintains the safety of pedestrians and cyclists as the highest priority.

“We want the vehicle to feel like a guest and for the pedestrian to be king on the street.” — Darren Enns, planning director, Town of Banff

Silva Cell installation, Sept. 2020: 3X stack of Silva Cells

Embodying the natural beauty of cascading mountains and the National Park surrounding the town, designers The Tula Project incorporated 92 street trees into the redesigned Bear St. space.

Kelsi Hurlbut, lead landscape architect at The Tula Project, wanted 92 street trees along three blocks between Caribou and Wolf streets to help bring the experience of the national park into the Town. WSP and The Tula Project helped realize that vision. All Silva Cells and trees were installed and planted by Bremner Engineering & Construction Ltd.

In total there are a combination of 687 3X, 2X, and 1X Silva Cells underground that will enhance ecosystem services for the entirety of the trees’ lives. The 90 trees have a grand total of 23,500 ft3 (666 m3) of soil volume for all of the trees’ roots.

2020 proved to be a good time to institute the $9.5 million reconstruction project of Bear St., as lockdown kept many tourists away because of COVID-19. Digging up and redesigning the road during this time was optimal.

Bear St. in 2021: post-construction. Photo courtesy of Calgary Herald

Accessibility, Usability, and Safety Are Key

The redevelopment of Bear Street as a “shared street” was intended to create a welcoming environment where pedestrians and cyclists are primary users and vehicles are made to feel more like the guests.

There are no curbs between the streets and the sidewalks so cars and cyclists and pedestrians can all seamlessly use the same space. The traffic-calming features extend to all of the paved space.

In the curbless environment, crossing is encouraged in all locations, travel lanes are not designated, and grades trend toward a trench drain that is flush with the surface to provide an uninterrupted level space accessible to all while accommodating drainage. Street trees create a beautiful canopy for the ample amenity space, which is populated with both private and public flexible site furniture. Soil cells have been installed to provide adequate soil volumes to support healthy tree growth and facilitate on-site stormwater treatment and management.

Image of town of Banff, courtesy of Dark Horse Company

The Power of Silva Cells: Saving Time, Energy, and Cost

All 687 Silva Cells and the adjacent planters collect stormwater from trench drains, filter it, irrigate the 92 new trees and all landscaping, and clean drainage before allowing it to flow into the stormwater system. Installed about 400 mm below ground, the Silva Cells are providing 4X the amount of soil than traditional open planters provide.

There are moisture sensors in the planters as well as in the Silva Cells. The moisture sensors connect to the irrigation system to tell it when to turn on during drought periods. Subsurface drip irrigation was introduced below the paver in the Silva Cell areas to maintain saturation under the pavers and promote root growth into the Silva Cells. The drip irrigation is on a different circuit than the planters so there are moisture sensors tracking each space.

Silva Cell installation, Sept. 2020: 3X stack of Silva Cells

“WSP, The TULA Project and Deep Root’s collaborative design approach was applied to Bear Street in the Town of Banff as an alternative way to reduce, manage and treat stormwater prior to the ultimate outfall at the Bow River, while providing sufficient uncompacted soil volumes for tree growth. The Town of Banff proceeded with the use of Silva Cells in the project due to the dual use of stormwater treatment and supporting tree growth in a downtown area.”
Jessica Wheatley, P.Eng., PMP – WSP Project Manager
Kelsi Hurlburt, Principal LA, – The Tula Project

Silva Cell installation, Sept. 2020: 3X stack of Silva Cells

Upgrading an Outdated System Through Trial and Teamwork

A key intent of the project was to replace centuries-old sewer and water pipes. Silva Cells added capacity to the existing stormwater system. Trench drains directed surface runoff to the planters and Silva Cells that retain, detain and treat the runoff as well as watering the trees.

Trench drains are feeding Silva Cells and trees in the open planter.

Installation Summary:
Number of Silva Cells: 687 3X
Amount of soil volume total 23,536 ft3 (666 m3)
Number of trees and type: 92, variety of coniferous and deciduous  
Type of project:
Integrated trees and irrigation
Project designer: WSP, The Tula Project
Project contractor:
Bremner Engineering & Construction Ltd
Installation date of Silva Cells: 2020
Project timeline:  2020–2021

 

Header Photo courtesy of  Helen Pike/C