In 2020 a Lower Mainland Flood Risk Assessment was completed to inform the Lower Mainland Flood Management strategy initiative and to support governments and others with flood management responsibilities in their work. The risk assessment identifies potential impacts of flood hazards in the region on people and vulnerable assets (buildings, infrastructure and other things of value) to develop a regional baseline profile of flood risk.
Components of the Risk Assessment
Flood Scenario Analysis
The risk assessment evaluated 16 different flood scenarios of different magnitude and likelihood. There were eight scenarios for each of two types of flood:
- Spring freshet flooding on the Fraser River and
- Winter storm surge flooding along the coast and Fraser delta
Based on these flood scenarios, a vulnerability analysis was undertaken to estimate potential flood impacts across the Lower Mainland, based on best available and accessible data within the project timeline and budget. Five consequence categories were assessed:
- Tangible direct damages to buildings, contents and infrastructure
- Intangible community consequences
- Social vulnerability
- Environmental consequences and
- Lifeline disruptions.
Challenges and Limitations
Assessing flood risk is extremely complex. The consequences of flooding depend on:
- size of the flood, how far it will spread, how deep it will be and how long it will last
- location, elevation and resilience of buildings and infrastructure, and
- how prepared a community is for floods of different magnitudes, including the potential for failures in flood protection infrastructure
A flood risk assessment cannot therefore predict all impacts of a specific flood. Moreover, many consequences cannot be easily measured – such as impacts to human health and well-being; loss of cultural, archaeological and traditional use sites; and contamination of the environment.
Finally, limitations on time, budget and available data limit the level of analysis – so more work will be needed over time. Examples include flood risks associated with First Nations values, interests and assets; the natural environment; and additional types of critical infrastructure.
Risk Assessment Report
The Risk Assessment report was prepared in 2020 for participants in the Lower Mainland Flood Management Strategy work. The report sets out methods and data and summarizes the technical results. Governments and other organizations with flood management responsibilities in the region can also access a data portal for select scenarios. Contact the FBC flood team for more information.