Public Realm

Sustainable sidewalks

Although only a short stretch of enhanced public realm in front of a new development, the potential impact of the Lake Shore Sustainable Sidewalk Pilot Project is much bigger than its size.

Perched on the north side of a new condo, next to the traffic of Lake Shore Boulevard, this little pilot project has transformed a concrete-clad sidewalk along the east of the Boulevard and the elevated Gardiner Expressway to a more pedestrian-friendly frontage with curbside planting that attracts pollinators, permeable paving that absorbs stormwater, and a sign telling pedestrians there is more than meets the eye below the surface.

Managed by Waterfront Toronto from 2017-19, Dillon Consulting and West 8 Landscape Architecture prepared a vision, schematic design and costing, and an implementation strategy for the transformation of the corridor. A series of small-scale, early-implementation projects were planned to signal change in the rapidly urbanizing corridor and set the example for development frontages to follow suit. This pilot is the first of these projects—the outcome of over two years of design, difficult approvals, and coordination. Now constructed, it is monitored to test innovative elements of the design and help inform the future vision for the Lake Shore Blvd. East corridor.

Bees on newly planted Coreopsis verticillata, July 2022. IMAGE/ Sonja Vangjeli

The project is a good case study of the many barriers keeping green infrastructure from being implemented more broadly on urban streets. Adjacent to a high speed road, next to an elevated highway and an elevated rail corridor, few sites are more urban and challenging than this one. Underground concrete duct banks and oil-filled steel hydro conduits snake around each other, with standards for offset distances making it impossible to plant trees, and leaving little room for roots to establish. Fluctuating groundwater can rise up not far from the surface, and stormwater runoff from the overhead Gardiner often inundates the ground plane. Shade and wind are prevalent next to a tower, and noise, pollution, and winter salt abound from the roads. Beyond physical site challenges, there are also regulatory barriers, such as the need to have a concrete base under unit pavers, and the constraint of minimal gaps between pavers negating any potential for permeability. Even if planting and permeable pavers could be implemented, who would take care of them, and would they survive left to their own devices? This is the purpose of this pilot: to assess if a vegetated bio-retention curbside planter and permeable pavers on the sidewalk can mitigate stormwater runoff while sustaining a durable, low-maintenance, yet enhanced public realm.

Newly replanted bioretention pilot project at Lake Shore Blvd. East and Bonnycastle with TRCA STEP monitoring equipment, July 2022. IMAGE/ Sonja Vangjeli

The design process saw many iterations evolving constantly per site investigations, negotiations with utilities, City approvals, and construction constraints. This led to creative solutions to the challenges of the site and regulatory standards. For example, the unit pavers selected, called Hydropavers, are sponge-like and permeable throughout, requiring almost no gaps between them, and not relying on gaps for permeability. Under the pavers, an alternative sub-base solution called Permavoid provides a solid foundation to distribute loads evenly, avoiding differential settlement, while allowing water to flow through and providing void space for any excess water or ice formation in winter without causing heaving. The passive irrigation system sustains the plantings by drawing water from a nearby shallow catch basin and directing it to the planting soil through a perforated pipe. A lid and overflow to an adjacent catch basin allow for a way to shut down the system in the winter if the salt impacts are deemed too damaging for the plants. A sub-drain diverts excess water to the sewer to ensure plantings don’t get inundated. The plant palette selected had to be extremely tough and resilient to wind, shade, flood, drought, salt, and pollutants. Halophytic plant species such as sea thrift (Armeria maritima) were included to extract salt from the soil to help the plant community survive.

Newly replanted bioretention pilot project at Lake Shore Blvd. East and Bonnycastle with TRCA STEP monitoring equipment, July 2022. IMAGE/ Sonja Vangjeli

The pilot is continuously monitored by Toronto Region Conservation Authority (TRCA) Sustainable Technologies Evaluation Program (STEP) as part of the City of Toronto’s Green Streets pilot projects monitoring program. A series of monitoring wells, drain basins with weirs, and sensors connected to the monitoring station were integrated in the design to ensure system performance could be monitored and adjustments made based on actual observations. 

A lot of thought and effort has gone into this humble pilot, and its potential impact on sidewalk standards is significant. The monitoring will provide useful information on the stormwater performance, durability, and maintenance requirements of the bioretention system and permeable paving assembly. These findings will feed into the Green Streets standards currently under development by the City of Toronto, making it easier for future green infrastructure projects to get approved. It will contribute to a culture shift from engineered grey infrastructure systems toward nature-based, ecologically performative green infrastructure. The way we build urban infrastructure needs to change to integrate with ecological processes, rather than obstruct nature. This shift could be led by landscape architects.

Newly replanted bioretention pilot project at Lake Shore Blvd. East and Bonnycastle with TRCA STEP monitoring equipment, July 2022. IMAGE/ Sonja Vangjeli

On a mild winter day, the little Lake Shore pilot is still covered by a thin layer of white snow. It looks like the permeable pavement is working to drain puddles away from the surface and make it more accessible for pedestrians. It is a tiny change within a metropolis of aging infrastructure, but its impact is mighty.

Text by Sonja Vangjeli, OALA, CSLA, Senior Urban Designer, City of Toronto, previously Design Project Manager, Public Realm at Waterfront Toronto.