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River Forecast Centre put entire South Coast on ‘flood watch’

Flood watch ‘means river levels are rising and will approach or may exceed bankfull’ conditions
B.C.’s River Forecast Centre upgraded the South Coast to flood watch, including the flood-damaged Fraser Valley, as seen on the map in orange, after heavy rain is forecast for the weekend on Nov. 25, 2021. (River Forecast Centre)

Steer clear of fast‐flowing rivers and unstable riverbanks this weekend.

B.C. River Forecast Centre issued a flood watch Thursday (Nov. 25) for the entire South Coast, which includes the still flood-damaged Fraser Valley, as the upshot from all the rain expected over the weekend.

Forecasters upgraded the South Coast to flood watch using hydrologic models, and maintained the flood warning for Sumas River, after Environment Canada called for more atmospheric rivers of rain.

Fraser Valley rivers may have started to swell after the first rainstorm Thursday, but only to a magnitude that is considered “typical” for fall storms.

RELATED: Special weather statement for weekend rain

It’s the second atmospheric river event forecast for Saturday, Nov. 27, they’re watching, as it could be “problematic to flood response and recovery efforts” given the already damaged infrastructure in the region.

A flood watch “means that river levels are rising and will approach or may exceed bankfull. Flooding of areas adjacent to affected rivers may occur,” according to the forecast centre.

Rainfall amounts Saturday to Sunday in the Fraser Valley could be 60 millimetres up to 120 millimetres near the mountains.

“The second system arriving over the weekend will likely be more problematic,” said forecast centre notice. “It is currently forecast to have higher rainfall totals, warmer conditions resulting in additional snowmelt and will occur immediately after the current storm system.”

Flows could reach 10‐year to 50‐year levels (or higher) Sunday or Monday.

“Since rainfall totals are expected to be higher, and temperatures warmer by the weekend, there is a greater risk for a rain‐on‐snow event to melt much of the current snowpack, adding additional water into rivers and creeks,” according to the Nov. 25 forecast from the Forecast Centre.

A third atmospheric river is forecast to drench B.C. again on Tuesday or Wednesday (Nov. 30-Dec. 1), but it’s too far away for exact impact projections or severity at this point.

Flood levels on Sumas Prairie and on the Sumas River have been slowly receding but the extra runoff from all the weekend rain could slow the rate at which waters are receding.

RELATED: Pierce Creek in Chilliwack River Valley flowing again

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Watching the Vedder River rise on Monday, Nov. 15, 2021. (Jenna Hauck/ Chilliwack Progress screenshot)

Jennifer Feinberg

About the Author: Jennifer Feinberg

I have been a Chilliwack Progress reporter for 20+ years, covering the arts, city hall, as well as Indigenous, and climate change stories.
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