Chilliwack under serious threat in Fraser River flood scenario

The 1-in-500-year Fraser River flood scenario, which would inundate much of the City of Chilliwack, is only becoming riskier as a result of climate change, according to the Fraser Basin Council. - Fraser Basin Council
The 1-in-500-year Fraser River flood scenario, which would inundate much of the City of Chilliwack, is only becoming riskier as a result of climate change, according to the Fraser Basin Council.
— image credit: Fraser Basin Council

If a major Fraser River flood is to occur in the coming decades it could trigger losses upwards of $30 billion amounting to the costliest natural disaster in Canadian history.

That's according to a study out Monday and commissioned by the Fraser Basin Council (FBC) as part of a strategy on behalf of 43 government and private sector partners.

And thanks to sea level rise and climate change, the risk of such a flood is only on the rise.

“We now have a crisper picture of the evolving flood risk faced by the Lower Mainland and the chilling economic cost of inaction,” said Colin Hansen, chair of the FBC. “It’s time to kick into high gear, have all partners determine the best flood protection for the region, and roll out an action plan. We’re pleased that the Province of B.C. is showing strong leadership to support this work.”

That leadership, according to Hansen, who served as BC Liberal deputy premier from 2009 to 2011, is in the form of a $1 million contribution by the provincial government to support phase 2 development of the flood action plan for the area.

“All Lower Mainland municipalities are working hard on local flood protection priorities, and we’ll all do our part to keep communities safe from a catastrophic flood," said Jason Lum, a City of Chilliwack Councillor and Chair of the Flood Control and River Management Committee at the Lower Mainland Local Government Association. "I’m happy to see such wide, proactive collaboration through the Lower Mainland Flood Management Strategy to better quantify flood risks and set priorities. Today’s investment by the Province of B.C. is pivotal to the development of a region-wide action plan.”

The Phase 1 assessment looked at four sample flood scenarios: two coastal flood scenarios (present day and the year 2100) and two Fraser River flood scenarios (present day and 2100).

All are estimated to be a 1-in-500-year risk (or 0.2 per cent in any given year), which would be equivalent to the 1894 flood of record.

And while snowpack this season is light, Steve Litke of the Fraser Basin Council suggests that that floods previously thought likely to happen one in every 500 years may now happen more often, possibly as often as 1 in 100 years because of more rapid snow melts and heavier spring rains.

The present day Fraser River flood would result in an estimated cost of $22.9 billion, and in the year 2100 that jumps to $32.7 billion, admittedly rough estimates based on a range of assumptions.

"One assumption is that each of the flood protection dikes in the region would fail during a major flood and that flood waters would spread unimpeded," according to an FBC press release issued Monday. "[I]n fact, it is possible that some dikes will breach during a major flood, while others will not."

The analysis found that under this Fraser River worst-case flood scenario, Chilliwack General Hospital, Chilliwack Airport and many schools would be inundated, and that half the agriculture losses in the Lower Mainland are incurred in Abbotsford and Chilliwack.

A recent assessment carried out in phase 1 of the study by the Provincial Inspector of Dikes showed that 71 per cent of the assessed Lower Mainland dikes are vulnerable to failure from overtopping during a major Fraser River or coastal flood scenario.

The City of Chilliwack has been working on ensuring the Fraser River dikes are up to the new higher level of provincial standards.

Last summer, the city completed the controversial Young Road dike project, and currently the city is planning for the next phase of flood management along the Hope Slough to Chilliwack Mountain, an area also under controversy as the current dike runs through the Skwah Reserve, the raising of which the band council is not likely to allow.

Under the 1-in-500-year scenario, most of Chilliwack would be under water except the hillside areas and Sardis.

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