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”.
Climate Change is projected to have long-term and ever-increasing effects on communities and the environment. It is encouraging to hear that data gaps in the vulnerability assessment for the City of Greater Sudbury’s (CGS) drainage related infrastructure are being addressed to prepare for the predicted increases in the severity and frequency of extreme weather events associated with climate change.
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.