Case study: Understanding climate change impacts key to prioritizing drainage infrastructure projects in Vernon, BC

The City of Vernon, BC, Drainage Infrastructure Prioritization Plan is the 2020 winner in the asset management category of FCM’s Sustainable Communities Awards.

In recent years, the City of Vernon, BC, has been challenged by climate-related events, including flooding, landslides and wildfires. To mitigate future impacts, the City applied a climate change lens to evaluate the vulnerabilities of their drainage network. This enabled them to prioritize their flood mitigation planning process.

City used asset management approach to evaluate drainage system

The City of Vernon is located in the North Okanagan region of BC, where climate change projections show increasing precipitation and more frequent storm events that include heavy rain. By applying an asset management approach and assessing their drainage infrastructure through a climate vulnerability lens, the City developed a risk assessment framework, mapped overland water flow paths and developed a prioritized list of drainage projects that can be incorporated in the City’s capital planning.  

Detailed topographical imaging used to show water flow paths

To collect the information they needed to assess risk, the City partnered with a provincial initiative to capture LiDAR data (a digital mapping tool) for the entire Okanagan Lake watershed. This let them affordably access the data they needed to calculate the most likely water flow paths from the moment a drop hits the ground until it reaches a receiving body of water. By modeling a once-in-a-hundred-year rainfall event, the City predicted flooding and related impacts on infrastructure.  

Outcomes include protecting watershed and optimizing infrastructure investments

Almost all stormwater drainage in the City flows into creeks that lead to Okanagan Lake, and these streams have been shown to have poor water quality. The Drainage Infrastructure Prioritization Plan identifies and prioritizes works that will prevent further impact on the watershed and other natural assets, as well as critical infrastructure assets such as roads. Infrastructure that may be affected by climate change in the years to come is identified as higher priority, such as within environmentally sensitive areas, or proximal to areas of higher population. Overland flow paths through steep slopes that have the potential to cause erosion are also high priority for protection or improvement. Overall, the plan will help the City direct funds to projects that provide multiple benefits and reduce the highest risks. By linking the economic impact of drainage infrastructure failure to risk, the City can make better-informed decisions about infrastructure investments and the risks to service delivery.    

Data collection and management proved challenging

With nearly 5,000 individual storm sewer segments and 16,000 unique overland flow routes in the city, managing large amounts of data proved to be the project’s biggest challenge. The project team developed a methodology that combined GIS data with information from available reports and designs in order to estimate flow rates. While the method did not capture the subtleties of detailed hydrologic modelling, it was adequate for the comparative assessment required. Finding topographic data that covered the study area was another challenge, which the project team overcame through its partnership with the Okanagan Basin Water Board to capture LiDAR. In the future, the City expects to face challenges related to overland flow routes. With a high level of impervious areas in the city already, the city will have to inform residents and developers about how water moves through the region and work together with them to restore natural flow paths and protect existing ones.