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Gallant Avenue in North Vancouver: Silva Cells Improve Soil Conditions for Streetscape Trees

Streetscape improvement project embraces Silva Cells, realizing at-source stormwater benefits and providing mature tree with access to new soil volume

Overview

A two-phase upgrade project breaking ground in 2021, the streetscape improvements along Gallant Avenue in the Deep Cove neighborhood of North Vancouver made permanent a temporary outdoor space expansion initiated during the first months of the Covid-19 pandemic. From wider sidewalks to flexible spaces for parking and extended restaurant patios, the primary purpose of the renovation was to realign local traffic and utility patterns while also creating a more inviting, pedestrian-friendly outdoor space – complete with a series of newly planted street trees. The DeepRoot Silva Cell system provided the required soil volume for healthy root growth while also addressing a pair of site-specific obstacles: the existence of a large, preexisting tree (that project planners were able to keep after installing Silva Cells in the adjacent area) and the desire to use stormwater runoff to water the trees and enhance the stormwater management design.

Installation Summary

Number of Silva Cells: Phase 1: (132 3X / 26 2X) and Phase 2: (300 3X / 18 2X)

Amount of Soil Volume Per Tree: 15 m3

Number of Trees: 23

Type of Project: Streetscape, Stormwater, Integrated

Project Consultants (Engineers and Landscape Architects): Project 1 (Storm Sewer): Water Street Engineering / Fred Liu and Associates / Project 2 (Livable Deep Cove): Urban Systems / Hapa Collaborative

Project Contractor: Phase 1: Conwest Contracting and Phase 2: GPM Civil Contracting

Project Timeline: 2021-2023

The Projects

The two-block stretch of Gallant Avenue, between Caledonia Avenue Road and Banbury Road, in North Vancouver’s Deep Cove Village has gotten a makeover.

Two projects saw this transformation. The first project included the replacement of a storm sewer and outfall along Gallant Avenue from Gallant Creek west of Panorama Avenue and through Panorama Park. This project included the road rehabilitation of approximately 90m of Gallant Avenue, including new curbs, sidewalks, street trees, and Silva Cells.

Livable Deep Cove was the second project which transformed the one-block of Gallant Avenue from Panorama Avenue to Banbury Road into a “livable street.”

In the spring of 2020, a pedestrian zone was created on Gallant Avenue as a means of providing more outdoor community space during the early days of Covid-19. The south side of the street was closed, and additional patios and walking paths were set up for area visitors. Feedback from local residents on the street alterations was very positive — the District of North Vancouver thus applied for grant funding to overhaul the area permanently, receiving approval for $3.3 million in 2021.

Design features of the new road plan included new one-way traffic flow, flex zones to function as parking or public realm space, enhanced pedestrian crossings, upgraded lighting and furniture, removable bollards, permanent loading zones for commercials vehicles, and a selection of newly planted streetscape trees — which, in addition to providing a welcoming atmosphere to residents and tourists alike, would help manage at-source stormwater (a somewhat challenging logistical element, given the sloped elevation of Gallant Avenue).

Given the design team’s commitment to urban forestry, they likewise wanted to retain a mature, preexisting tree in the upper Gallant area whose roots were busting out of a small planter adjacent to the sidewalk. In response to these green infrastructure challenges, project planners turned to the DeepRoot Silva Cell for solutions.

DeepRoot Silva Cell Success

The first phase of the improvement project — the “upper” Gallant Avenue area — was completed in 2021 and utilized a total of 158 (2X and 3X) Silva Cells. Each of the 8 newly planted trees receive access to 15 cubic meters of soil volume, more than meeting local standards, to help guarantee long-lasting vitality and health.

A unique characteristic of this project was the preexistence of a mature tree — and the unanimous desire to keep it in place. It was originally planted without much foresight for root expansion, and the small planter and adjacent pavement buckled as the mature tree roots broke out of the small tree pit. The contractor was able to remove the adjacent sidewalk and planter wall and Hydrovac out the soil while retaining the important support roots (all completed under the watchful supervision of the district arborist).

Silva Cells were installed adjacent to the existing tree to create a new volume of soil into which the tree roots could spread. The contractor was then able to build the Silva Cells around the retained support roots system without damaging them, due to the modular design of the system. Finally, a new planter curb and sidewalk were poured over the Silva Cells, thus retaining a mature local tree in a new, and much larger, healthy soil environment.

The “lower” Gallant Avenue area, the second phase of this initiative, broke ground in the spring of 2023. Fifteen trees will access their soil volume from the 318 (2X and 3X) Silva Cells being installed. The Silva Cell system was also incorporated to enhance the stormwater plan. Silva Cells help reduce peak-flow water events, improve water quality by filtering it through the soil, and provide the necessary water to the growing tree roots.

Water enters the Silva Cell system from trench drains that run along the sidewalk and direct water into the cells. In the “lower” Gallant zone, the Silva Cell trenches are stepped to allow for a flat stormwater distribution pipe to distribute water evenly throughout the entire soil environment — indeed, the Silva Cell system can be installed on up to a 10% slope and still meet all of the H20 loading criteria of street engineers.

DeepRoot Silva Cells are proud to help contribute to this ambitious restoration project, providing residents and tourists with a more inviting experience in the Deep Cove neighborhood of North Vancouver.

Partner Testimonials

Michael James, DeepRoot general manager and project lead on the Gallant Avenue initiative, spent time with Spencer Thompson of Urban Systems and Chris McBride of Hapa Collaborative to get an engineering and landscape architecture perspective on the project — including its objectives, challenges, and the benefits of the Silva Cell system.

Project Objectives

What were the design and engineering goals of the Gallant Avenue project?

“The design intent was to provide a flexible, festival-style streetscape where parked cars could be moved on and off of Gallant Street during peak times of the year. With that, the street tree really became a key component – as integral as the paving materials and the site furnishings. We wanted to be sure we provided adequate and proper soil volumes and growing media to give us an idea that the trees would be thriving and healthy in the future.” -Chris McBride, Hapa Collaborative

“The design intent was established largely to enhance the public realm and the user experience of the street. And with that came a desire for large tree canopy and incorporating rainwater management features into the street.” -Spencer Thompson, Urban Systems

Project Challenges

What were some of the Gallant Avenue project challenges?

“The street itself was very constrained with existing utilities. There were existing utilities running down the street and utility crossings serving existing buildings that all needed to be managed.” -Spencer Thompson, Urban Systems

“The street itself was also fairly steep, at five to ten percent grade, which made it somewhat challenging to integrate the street trees with utilities and find a way to integrate the rainwater management component.” -Spencer Thompson, Urban Systems

Silva Cell Solutions

How did the Silva Cell system help you achieve your objectives and solve project challenges?

“Helping us to solve all of these constraints, and try to meet the project objectives, led us to the Silva Cell solution which allowed us to achieve the desired soil volumes within a fairly congested street with all of the utilities and trying to achieve the public-realm enhancements.” -Spencer Thompson, Urban Systems

“What was helpful in this approach was involving the manufacturers as part of the design process to get their take on these systems – particularly the Silva Cell system and what is doable with them, what has been done in the past, what they’ve seen from project successes, and different types of configurations in similar environments with these types of constraints in built-out urban environments with utilities.” -Spencer Thompson, Urban Systems

“For us as landscape architects, there’s only so much we know. Having the ability to work with DeepRoot directly early on in the project allows us to better understand what the parameters are and what the restrictions are with the system and work through some of the intricacies, so we know, come construction, we’ve resolved all those concerns.” -Chris McBride, Hapa Collaborative

“With the trees, there was a desire to have large trees and healthy trees, and that’s where we’ve integrated the Silva Cells to achieve the desired soil volumes for the street trees as well as trying to irrigate or water the trees with the rainwater runoff from the street through a series of pipes to the street trees.” -Spencer Thompson, Urban Systems

“We always knew that the street tree would be an integral part of the project. So, from early on, we were engaged with DeepRoot and worked with [Urban Systems] to ensure that we had adequate soil volume, the right growing media, and that we were able to work with the rainwater calculations and rainwater harvesting to ensure the site drainage was being diverted back into the Silva Cell system.” -Chris McBride, Hapa Collaborative

“Having the flexibility that DeepRoot provides us allowed for an ease of construction – we were able to use one or three of the modules to build up and work around existing utilities on the site.” -Chris McBride, Hapa Collaborative

“We arrived at the Silva Cell solution, which also allowed us to come up with custom designs. It’s a modular system, so we were able to work with the cells at different spacings to accommodate existing utility crossings and also step the cells vertically to achieve the grade changes we were dealing with across the street. And stepping those cells vertically allowed us to keep the cells at a relatively flat grade – even though the street itself is sloping quite a bit. That helped with the rainwater management and the irrigation of the trees that we were trying to achieve. That allowed us to use flat pipes for distributing water into the Silva Cells as well as draining water out of the Silva Cells. So, having that flexibility to step the cells vertically – and while doing that, still have spacings for utilities – was critical to the project success.” -Spencer Thompson, Urban Systems

Additional Resources

Check out other DeepRoot projects in North Vancouver here and here.

 

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