Resources are available to guide staff, engineering consultants, contractors and members of the public when planting, designing or constructing green streets systems.
The Province of Ontario, Toronto and Region Conservation Authority, and City of Toronto have a shared interest and responsibility to promote and expand green infrastructure.
Provincial legislation, official policies and design standards direct the City to enhance the longevity of the urban forest, mitigate the urban heat island effect, manage stormwater runoff to mitigate flooding and enhance water quality, promote infiltration to sustain shallow groundwater systems, and enhance air quality.
Green infrastructure can help satisfy these objectives with passive techniques that are introduced incrementally and at different scales of intervention. Green infrastructure can help build a Toronto that is resilient to climate change and improve overall quality of life.
Green streets supports the City’s Resilience Strategy, Wet Weather Flow Master Plan, Toronto Green Standards, Pollinator Protection Strategy, Biodiversity Strategy and other City policies and strategies.
Continuous Soil Trenches (CST) and Stormwater Tree Trenches (STT) are trenches that exist beside sidewalks, roads, and other walkways that channel stormwater into planters in order to promote tree growth and other plants. In standard conditions, growing a tree to its fullest is a tedious task that requires lots of maintenance, especially when it comes to watering the tree. STT’s reduce the external dependency of the tree by providing an autonomous and resourceful means of hydrating the tree.
A portion of the surface runoff is absorbed by the plant to diminish the amount of stormwater entering the trench. Within the right-of-way, some of these tree planting areas are supported by additional infrastructure in order to purposefully manage stormwater runoff.
Sod boulevards are challenging growing environments for street trees. These trees are susceptible to drought, vandalism, vehicular collisions, salt spray, utility line clearing, and damage from construction, lights and signs. Trees growing in paved boulevards are also exposed to these challenges have the additional limitation of a lack of high quality soil to support their establishment and growth. Without careful design and construction, these trees experience relatively higher mortality and typically enter into an on-going cycle of removal and replacement.
Bioretention assets are dips in land that allow surface runoff to be deposited into a garden-like structure. From this garden like structure, part of the water is sent into a sewer systems while a portion of the water is used to nurture plants native to the area.
In softscapes, bioswales are typically linear vegetated channels that convey, treat and temporarily store stormwater runoff. To provide filtration, temporary storage and infiltration, its subsurface composition consists of a filter media, drainage layer and underdrain depending on native soil infiltration rates. Vegetation may be incorporated to reduce the velocity of runoff and promote sedimentation, filtration, evapotranspiration and infiltration. Multiple inlets may be installed along the length of the bioswale while a downstream outlet structure is required to convey excessive flows from large storms to an adjacent drainage system.
In hardscapes, bioswales areas are gently sloping, depressed planting beds or similar concrete structures that convey, treat and temporarily store stormwater runoff. To provide filtration, temporary storage and infiltration, its subsurface composition consists of a filter media, drainage layer and underdrain depending on native soil infiltration rates. Vegetation is incorporated to reduce the velocity of runoff and promote sedimentation, filtration, evapotranspiration and infiltration. Multiple inlets may be installed along the length of the bioswale while a downstream outlet structure is required to convey excessive flows from large storms out of the system and back to the roadway or an adjacent drainage system.
Enhanced grass swales are a more subtle version of swales, which involve a channel with a miniscule slope to appear flush with the grass surface that surrounds it. The gentle slope along with the vegetated channel and soils assist in reducing stormwater runoff and runoff treatment with respect to water quality.
Green gutters are shallow vegetated planters that extend along the length of a street and are typically used to separate corridors for different modes of transportation, such as between cycling, vehicular and Light Rail Transit. Curb inlets located at intervals along its length convey roadway stormwater runoff into the system while vegetation and filter media act to reduce, filter and infiltrate the runoff. Outlets are located at the downstream terminal of the green gutter to convey any excess runoff back to the roadway.
Vegetated filter strips are gently-sloping, densely vegetated areas that treat runoff as sheet flow from adjacent impervious surfaces such as roadways, sidewalks, driveways and parking lots. These systems are typically made up of a layer of growing medium with increased water-retaining properties to reduce runoff and enhance sedimentation, filtration, infiltration and evaporation. Filter strips may function as a stand-alone feature or as pre-treatment where excess water can be conveyed to other adjacent green infrastructure or drainage systems.
Permeable pavements consist of joints and/or pores that allow rainwater and snowmelt to drain through the surface and be temporarily stored within an aggregate storage layer. Water can then be infiltrated into the underlying native soil or conveyed to other drainage systems via an underdrain. The functionality between the various types of permeable pavements remain the same, but the primary difference is in the surface composition, as follows:
Infiltration trenches consist of geotextile-lined excavations filled with aggregate that temporarily stores stormwater. The temporary storage within the trench allows for the treatment and infiltration of stormwater into the underlying native soil. Stormwater runoff may be conveyed into the system through inlets including curb cuts or similar concrete structures and drains or pipes connected to stormwater infrastructure. Another application is infiltration galleries, which are placed beneath permeable pavement to allow runoff to percolate into the storage area beneath. Depending on the infiltration rate of the native soil, an underdrain may be installed to collect and discharge excess water to adjacent drainage systems. Vegetation may also be planted around the vicinity of the trench to enhance the system’s aesthetic appeal.
Rain gardens are sunken planting beds constructed of highly permeable nutrient rich soils. They can include an engineered soil layer and overflow structure to increase their stormwater management performance. Rain gardens should always be designed to drain efficiently after a storm event to avoid creating areas of standing water where mosquitoes can breed. They are well-suited to suburban neighborhood street types and can be installed within planting zones, medians and islands.
Individual property owners may be interested in planting horticulture, other than sod, within the boulevard area fronting their property within the right-of-way.
Requirements for planting within the boulevard are:
For projects that extend beyond your own boulevard and fall into one of the categories below, read about the PollinateTO program. Grants may be available for those who apply and qualify.
A technical manual, standards, specifications and construction drawings are available to guide the technical design, construction, maintenance and monitoring of Green Streets. These resources are written for City staff, developers and consulting engineers involved in green streets design as a part of road works projects.
Toronto’s Green Streets Technical Guidelines provide guidance, standards and selection tools for the planning, design, integration and maintenance of a range of green streets options appropriate for the street types and conditions.
The guidelines are meant to be a tool for City staff, developers and consultants with the key objectives of providing an understanding of sustainable stormwater planning and practices, informing the selection of appropriate green streets options to be integrated as part of street retrofit/rehabilitation or new/reconstruction projects and ensuring that green street designs are attractive, functional and appropriate to their urban context.
Design options for Tree Planting illustrate how hard surface environments can be designed to achieve the higher soil volumes necessary for tree growth and survivability, stormwater management, and facilitate utility subsurface access and maintenance activities.