Lower Mainland Flood Risk Assessment 

The Lower Mainland Flood Management Strategy (LMFMS) places an emphasis on reducing flood risk across the Lower Mainland region. A key input to this work is a Lower Mainland Flood Risk Assessment.

The risk assessment spans BC’s South Coast — from Lions Bay to White Rock — and covers the lower Fraser River — from Hope to Richmond. It evaluates the potential impact of the region’s flood hazards on people and vulnerable assets (buildings, infrastructure and other things of value) to develop a regional baseline profile of flood risk. With this risk profile, the LMFMS partners and decision makers will gain a better understanding to inform flood risk management across the region.

Objectives of the Risk Assessment

  • Broaden and deepen the understanding of flood risk in BC’s Lower Mainland; and
  • Support risk-based decision-making for the broader Lower Mainland Flood Management Strategy, in particular by identifying higher risk areas of regional priority for flood risk reduction. 

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:

  1. Spring freshet flooding on the Fraser River and
  2. Winter storm surge flooding along the coast and Fraser delta. 

Vulnerability Analysis

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: 

  1. Tangible direct damages to buildings, contents and infrastructure
  2. Intangible community consequences
  3. Social vulnerability
  4. Environmental consequences and
  5. Lifeline disruptions.

The results of this assessment will be included in a draft LMFMS report in summer 2020.

Challenges and Limitations

Assessing flood risk is extremely complex. The consequences from flooding are highly dependent on:

  • geography
  • size of the flood, how far it will spread and how deep it will be
  • the location, elevation and resilience of buildings and infrastructure, and
  • how prepared a community is for floods of different magnitudes. 

A flood risk assessment cannot therefore predict with precision all impacts of a specific flood event. Moreover, many flood 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 – it is anticipated that more work will be done over time.

Value of the Assessment

The risk assessment is an important step in understanding the value of assets at risk in the Lower Mainland.

The flood hazard model, flood damage model and risk profile tool that have been developed can all be refined with additional data and analysis, including additional flood scenarios, to continue to improve our understanding about flood risk across the Lower Mainland and inform risk reduction policies and actions.