Significant Flood Risks Found for the Lower Mainland,
British Columbia

A new study shows flood risks in the Lower Mainland region of British Columbia are significant and will become more severe as a result of climate change, indicating an urgent need for developing a flood management strategy. The study, conducted for Fraser Basin Council by a team led by Northwest Hydraulic Consultants (NHC), estimated potential current and future losses for Fraser River and coastal floods. Losses from riverine floods would be somewhat higher than for coastal floods, and a recurrence of the 1894 flood of record would result in more than $20 billion in economic losses today, increasing to over $30 billion at the end of the century.

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Lower Fraser River at Alex Fraser Bridge,
looking upstream
Fraser Basin Council held a briefing session on May 30, 2016 to publicize the results of the Phase 1 Lower Mainland Flood Management Strategy. The flood strategy will enhance protection for communities along the Lower Fraser River from Hope to Richmond and on the coast from Squamish to White Rock. Nearly 500,000 people of the regional 2.8 million population live in flood-prone areas. NHC worked on the two key projects for Phase 1 - a flood vulnerability assessment for the region and an evaluation of present dikes to withstand a major flood.



NHC mapped the extent and depth of flood inundation using geographic information systems (GIS). The Hazus-MH 2.1 Canadian Flood Module was used to estimate losses related to residential, commercial, and public/institutional buildings. Infrastructure, cargo shipping delays, and agriculture losses were estimated outside Hazus. NHC's final report is available at this link.

The Lower Mainland region is protected from flooding by a system of 74 dikes that extend over a length of
500 km. The NHC team reviewed not only the adequacy of dike crest levels but also geotechnical stability, erosion protection, control of vegetation and animal activity, building encroachments, associated structures, and administrative arrangements such as right-of-way agreements, maintenance procedures, and emergency preparedness. Only 13% of the dikes were classified as being in fair to good condition, while the remainder were poor to unacceptable. The NHC dike assessment report can be downloaded at this link.

The studies have improved our understanding of regional flood risks and will support development of a flood management strategy that incorporates structural and non-structural measures, an implementation action plan, and recommendations for a secure, sustainable funding model. For more information please contact Monica Mannerström, PEng via email.

Sample flood depth map for Richmond and Delta assuming dike breaching.
(Dark blue area represents flood depth of 2-5 m, light blue 1-2 m, green 0.5-1 m, and yellow 0-0.5 m.)