If the design objective is to meet and provide peak flow control for storm events, it is necessary to plan beyond the 1:100-year peak flow, and instead plan for the new norm of a 1:1000-year flood event. Planning for the appropriate peak flow is crucial to building climate resilience and meeting the demand over the full lifecycle of the infrastructure. If an inadequate peak flow formula is used it could result in significant additional costs to the City if it has to repair or tear up failing infrastructure to rebuild and increase capacity before it has reached its end-life. “Even a 1000-year return period has a 5% risk of being equalled or exceeded in a 50-year period.”
The Report indicates that “the anticipated influence of climate change on precipitation is steeped in uncertainty with future projections ranging from a minimal increase to almost a 250% increase”, and yet the stormwater planning only ranges from a 1:5 to a 1:100-year flood event. The Report admits that “this range represents a significant challenge to the municipality to understand and integrate into its planning decision making process”.
The extremes of climate change will affect the operation of critical infrastructure such as water and wastewater treatment plants, sewers, the electrical grid, public transport and roads that are sensitive to temperature and weather thresholds. Beyond these thresholds, infrastructure may have reduced capacity or may not function at all.
The ECO’s report listed 44 municipalities across Ontario that continue to use Combined Sewer Systems (CSSs); however, the City of Sudbury was not included in that list in spite of the fact that we have several wastewater treatment plants (WWTP) with CSSs within the Vermilion River Watershed.
It is also important to emphasize the importance of planning for a warming climate by building resilience into whichever alternative/s are chosen. In this vein, planning should be based on at least a 1:200-year storm event, and preferably a 1:1000-year flood event for true resilience to climate change.
These Public Information Centre panels are very high level, so at this time there isn’t too much to comment on; however, it is important to consider the Chelmsford Wastewater Treatment Facility in this assessment.
The importance of creating, maintaining and protecting natural infrastructure such as wetlands, swales and vegetated buffers cannot be overstated when it comes to flood management and filtering stormwater runoff. Policies supporting this concept would go a long way towards reducing some of the stormwater infiltration into the wastewater collection systems.
Watershed and subwatershed studies should include water quality and water quantity considerations to help maintain and enhance natural freshwater systems, including fisheries and aquatic habitat. These considerations should be guided by commonly accepted and held principles, including an ecosystem-based approach, a landscape-based analysis, cumulative effects, the precautionary approach, adaptive management, and sustainable development.
What are the goals and objectives of this study? There is very little information about the subwatershed study, but instead appears to be primarily designed to manage stormwater run-off to prevent flooding and development impacts.