Ottawa's tree canopy is facing devastating loss: mature trees are being lost to urban development and sprawl, spaces for trees are under severe pressure from growing intensification, young trees are not surviving due to poor growing conditions and poor planting practices, and thousands of trees have been knocked down in the last two years from accelerating local impacts of climate change, including intense wind (the derecho May 2022), heavy rain and flooding (August 2023), and ice storms (April 2023).
Ottawa must ensure that our city's infrastructure and tree canopies are equipped to withstand the intense rainfall we are expected to see in coming years.
Despite the fact that trees and pervious green spaces are among the most impactful and beneficial methods to managing rainwater, the City of Ottawa's Infrastructure Master Plan continues to prioritize retrofits to the drain systems (aka "grey infrastructure") over nature-based solutions.
CAFES has been advocating for the City to adopt Stormwater Tree Trenches (STTs) as a green engineered stormwater management solution. STTs exist beside sidewalks, roads, and other walkways and are composed of trenches with trees planted in soil cells or structural soil that that use inlets, perforated pipes and catchment basins to channel stormwater into the tree planters, filter run-off, replenish groundwater and promote tree growth.
STTs are highly effective at managing overland flooding during rainfall and reducing the amount of rain entering into the City's drain pipes, which are often at-capacity during heavy rains. Because STTs reduce the external dependency of the tree by providing an autonomous and resourceful means of hydrating the tree, STTs can lead to healthier, stronger tree canopies.
Many cities have adopted the use of STTs and follow specific technical guidelines for their construction and implementation, including the City of Toronto and the City of Vancouver. The City of Vancouver's Rain City Strategy demonstrated that STTs are not only effective at capturing 72-87% of total rain volume and reducing the amount of rain going into drains by 60%, but they are cheaper in the long run compared to the high costs of regular storm drain repairs and maintenance.
On June 20th, CAFES gave a public delegation demonstrating the benefits and cost effectiveness of STTs at the City's Joint Planning and Housing and Environment and Climate Change Committee, which discussed the Stormwater Management Plan as part of the Infrastructure Master Plan. As a result, Councillor Johnson put forward an inquiry to staff to further investigate the cost benefits of implementing STTs in Ottawa.
See our presentation below. You can watch the delegations and committee meeting on YouTube here.
STTs are just one example of the integration between trees and climate resilience. Incorporating climate resiliency into urban forestry involves strategic planning to ensure trees will survive despite climate changes. For example, street trees need to be planted in appropriate soil volumes to ensure they are well-rooted and sturdier in major winds. This may also involve choosing urban tree species that tend to form deeper root systems. The species of trees chosen should be intentional, with priority given to hardy, salt and pollution tolerant trees that are native to this region.
Organizations and other municipalities have also been looking into “near” native tree species, or Carolinian species, which have adapted to slightly warmer climates south of the Canadian border and may be well-suited for the warmer climate that Ottawa can expect in the coming decades (while still being suitable habitats to support Ontario’s biodiversity).
If you are interested in these issues or have experience working in the areas of climate resilience, stormwater management and tree canopy, please reach out to us at info@cafesottawa.ca.
