Lower Fraser Flood Model
Early Flood Profile and Dike Design
According to the Province, there is now $50 billion worth of development in the Lower Mainland floodplain that relies on dikes and other flood protection infrastructure.
The majority of today’s flood works were constructed by the federal-provincial Fraser River Flood Control Program between 1968 and 1995.
In 1969 the federal Inland Waters Directorate established dike design levels based on the estimated flood water levels plus 0.6 m of freeboard. At that time, authorities relied on high water marks from the two largest floods on record, in 1894 and 1948, and limited modelling to create the flood profile. Other flood management plans and decisions also relied on the 1969 profile. Engineers of the day did not have access to sophisticated data-gathering and analytical tools, however. Nearly 40 years later, a new study was needed to bring the flood profile up to date.
Updating the Flood Profile — Results and Implications
In 2003 the Fraser Basin Council and the BC Ministry of Environment initiated a multi-year study to develop a hydraulic model of the lower Fraser River to update the flood profile. The study, managed by the Fraser Basin Council, was intended to develop a flood profile based on:
In November, 2006 the results of the study were released. The flood profile computed by the Lower Fraser hydraulic model was higher than the original 1969 flood profile. As a result, the study found that widespread dike overtopping and dike failures would occur throughout the Lower Fraser River should there be another major flood equivalent to the 1894 flood of record. In such an event, diking systems from Chilliwack and Kent to Surrey and Coquitlam would be overtopped at one or more locations, and the Delta dike at Fraser Shore would be overtopped at one location. Freeboard for a winter storm surge flood would be inadequate in Delta and Richmond. The flood model was further updated in 2008 with data from the 2007 freshet.
Work on BC’s Dikes
Following the flood study, the Province adopted a new flood profile for dike design and construction. In March, 2007 it provided $33 million for diking authorities throughout BC to undertake urgent flood mitigation works for completion prior to the spring freshet. The Province subsequently announced an intention to invest $100 million over 10 years for flood protection infrastructure and maintenance.
Additional work has since been done by provincial staff on BC’s sea dike design guidelines and coastal flood hazard management. This is critical for low-lying coastal communities in BC as sea level is projected to rise resulting from climate change. Read about it.