The threat of a major flood in the Lower Mainland is not to be taken lightly.

A briefing paper for the climate action committee of the Metro Vancouver regional district spells out what could happen if a major Fraser River or coastal flood were to occur between now and 2100.

The document prepared by the Fraser Basin Council notes that a major flood could “trigger losses estimated at $20-30 billion”.

According to the document, this could “become the most costly natural disaster in Canadian history”.

“Vulnerabilities include risks to life, flood damage to buildings and critical infrastructure, business and service disruptions and estimated displacement of 250,000+ residents,” the paper states.

The briefing paper was put together by Steve Litke, senior program manager with the Fraser Basin Council.

The document states that the Lower Mainland region “faces a significant and growing risk of a large-magnitude flood”.

“Climate change projections show that an increase in frequency and severity of both coastal and Fraser River flooding is expected by year 2100,” the briefing paper points out.

Litke was invited to make a presentation to Metro Vancouver’s climate action committee at its meeting on Friday (March 13).

On its website, the Fraser Basin Council recalls that the largest Fraser River flood on record was in May  1894.

The event was caused by a rapid snowmelt that “caused river levels to rise dramatically, triggering flooding from Harrison to Richmond”.

Property damage was limited because settlement was sparse at the time, according to the nonprofit.

The next largest Fraser flood of record was in 1948, causing impacts that were greater than 1894.

According to the group, the B.C. provincial government tallied $210 million in damages from the 1948 flood.

Some 16,000 people evacuated, and around 2,000 homes were damaged or completely destroyed in that disaster.

The briefing paper by Litke notes that the 1894 Fraser River flood of record is a one-in-500-year event, and could happen again by year 2100.

According to the document, majority of flood dikes that were built decades ago are not going to provide adequate protection.

“A recent evaluation shows that most would fail during a recurrence of the 1894 Fraser River flood of record,” the briefing paper states.

The paper notes that a region-wide flood strategy is currently being developed.

The program involves federal, provincial, and local governments, as well as First Nations, and private and public-sector organizations.

A draft strategy is expected to be available in spring 2020.

An analysis of flood hazards and state of protection was completed in 2016, constituting phase one of the strategy.

A Fraser Basin Council report on the said assessment notes that a 2015 review shows that 71 percent of flood protection dikes evaluated are “vulnerable to failure by overtopping during either a major Fraser River or coastal flood”.

A total of 74 dikes were evaluated, representing 50 percent of all dikes in B.C.

The 74 dikes stretch 500 kilometres.

“A key reason that Lower Mainland dikes are considered vulnerable to failure is because most were reconstructed in the 1970s and 1980s according to the standard of the day, which has since been recognized as too low,” according to the report.