When renewing downtown Oakville’s streets, street pits for trees will be constructed in accordance with best practices to ensure health and longevity.
Tree pits in the study area utilize: Soil Cells. Soil cells promote mature and healthy street tree growth by providing a space for soil that is protected from compaction.
The space can be underneath any pavement structure in the right of-way including sidewalks, curbs and parking lanes.
If detailed correctly, tree canopies will grow taller and fuller.
This technology can also accommodate underground utilities, making it ideal for enhanced streetscapes in constrained corridors. Per tree soil volume targets is established in the Urban Forest Strategic Management Plan (2008).
These standards may require additional review to inform the detailed design of tree pits.
The North Oakville Urban Forest Strategic Management Plan (2011), for example, targets a minimum volume of 30m3 of high-quality soil per tree if in a single planter or 15m3 per tree if in a shared planter.
Soil cells are more expensive to install than traditional tree pits but offer numerous advantages as a healthy urban forest improves air quality, reduces wet-weather flows, moderates climate, stores and sequesters carbon, and can increase property values.
In addition to soil cells below grade, tree pits open at grade (i.e. - no tree grates) providing the best possible growing conditions for trees.
These open pits should be raised, as shown, and can be mulched or planted.
Using stormwater to passively irrigate street trees is a sound use of a readily available resource. Stormwater is directed into tree pits in lieu of a mechanical irrigation system. Stormwater that enters tree pits can then infiltrate into surrounding soil.
A weeper system should be integrated into the tree pit to intercept water during larger rain events and to prevent water from ponding in the pit. Water can enter the tree pits via an area drain system, a rill drain system or via permeable pavement in the street tree and furnishing zone.
Additionally, water will enter the system through the open tree pit areas. Monitoring wells should be installed periodically to allow for performance monitoring.
What are Silva Cells, and how do they work?