Fraser River Flood Risk Report

Canada’s federal Senate Committee on Agriculture and Forestry has released a report on flood control in BC’s Fraser Valley with advice and a warning from Northwest Hydraulic Consultants (NHC): if the Fraser River were to overflow its banks in the future, the extent of damages would be at least tenfold greater than the devastating effects experienced in the November 2021 floods. NHC staff were among 23 expert witnesses advising the Senate Committee investigation into the significant rainfall events in November 2021. Extensive flooding in southwestern BC’s Lower Mainland region affected more than 1,000 farms, 15,000 hectares of land, and 2.5 million livestock, as well as road and railway infrastructure.

In testimony at the Senate Subcommittee hearings into the floods and recovery efforts, an NHC team representative explained that the BC floods in November 2021 were not the result of the Fraser River overflowing its banks. The extensive rainfalls caused high stream flows and floods in the Nooksack and other rivers in the region. The situation would be much worse, NHC has warned, if the Fraser River overflows its banks; the resulting damage would be at least tenfold greater than the damage caused by the November 2021 floods. Given the potential for the Fraser River to overflow its banks in the future, updates to the flood emergency preparedness plans are urgently required.

For decades NHC engineers and geoscientists have been studying the Fraser River on behalf of local, provincial, First Nations, and federal governments. In 2015, a team of NHC hydrotechnical engineers and flood hazard and mapping experts conducted a dike assessment study and concluded that the dikes in BC’s Lower Mainland region, from Hope to the Pacific Ocean, were no longer meeting the increasingly more stringent provincial standards for dike design. The NHC specialist team concluded that 87% of Lower Mainland dikes are in less-than-fair condition and 71% would fail simply by overtopping during a flood event. Other flood management specialists from outside NHC support these conclusions.

NHC acknowledges that raising dikes and upgrading pump stations would be very costly, but regardless, governments should prioritize these upgrades and explore additional flood mitigation measures. NHC representatives have also suggested that the International Joint Commission could resolve the transboundary water issues involving the Nooksack River to help mitigate future flood impacts.

The report, Treading Water: The impact of and response to the 2021 British Columbia floods, outlines the committee’s findings from its study of the floods’ impact and the subsequent recovery efforts, as well as the lessons learned that the committee identified.