Gallant Avenue in North Vancouver: Silva Cells Improve Soil Conditions for Preexisting Tree

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 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 Landscape Architect: Phase 1: Hapa Collaborative and Phase 2: Urban Systems

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

Project Timeline: 2021-2023

The Project

The two-block stretch of Gallant Avenue, between Banbury Road and Panorama Drive, in North Vancouver’s Deep Cove Village is getting a makeover.

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, 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.

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 in this area was brought into the Silva Cells from a combination of catch basins and bump-out gardens.

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, is breaking ground in the spring and summer of 2023. Much like its first-phase counterpart, phase 2 is using stormwater to water the trees, which takes pressure off the gray infrastructure stormwater system. Fifteen trees will access their soil volume from the 318 (2X and 3X) Silva Cells being installed. Water will enter 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.

Additional Resources

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