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Prepare for rain: Atmospheric river forecast to hit Island

Downpours fuelled by warm tropical air and moisture are expected to start Thursday and deliver 40 to 80 mm of rain along the west coast of Vancouver Island, and five to 20 mm on the eastern side, from Victoria to Campbell River.

After months of record dry conditions, it’s going to get really wet — really fast — on most parts of Vancouver Island this week.

The dreaded term “atmospheric river” has returned to our world, with Environment Canada predicting those concentrated funnel downpours — fuelled by warm tropical air and moisture — will start Thursday and deliver 40 to 80 millimetres of rain along the west coast of the Island, and anywhere from five to 20 mm on the eastern regions from Victoria to Campbell River.

Heavy rains will ease to showers on Friday, but the rain’s intensity is expected to increase late Saturday and into Sunday, with continued showers into next week, said Derek Lee of Environment Canada.

It’s not enough to issue an alert at this point, Lee said Wednesday, but the rainfall will certainly be an eye-opener.

“It is potent, but it’s also typical for this time of year,” said Lee. “Atmospheric rivers come in different sizes, durations and intensities. This one will not be as long as some of the atmospheric rivers we saw last November, which caused a lot of the damage last year.”

For Tammy Calverley, who manages Russell Farm Market near Chemainus, the term atmospheric river brings a shudder.

The market has been flooded and severely damaged twice in the past two years as the Chemainus River overflowed its banks amid heavy rains, deluging the buildings in more than a metre of water and depositing thick river silt that destroyed food, refrigeration units and structures. It happened last November and before that in February 2020.

Every time rain is forecast, Calverley looks to the skies and holds her breath. “We’re really at the mercy of Mother Nature here,” said Calverley, whose property sits in a bowl and is uninsurable for floods.

The market owner is still awaiting $25,000 from Emergency Management B.C. in compensation for damage from last November’s massive storms. The claim is still working its way through the system, said Calverley, and the market continues to struggle to make ends meet.

This fall, however, there is some hope that work on the Chemainus River will improve the situation.

Crews were on the river Wednesday to level mounds of gravel from previous floods and the banks are being shored to prevent a mass spill into the flood plain, which includes the market property.

Calverley also said most logging in the surrounding mountains has ceased. She blames debris from those operations for some of the flooding, as it clogged some areas of the river near the highway bridge.

Emergency Management B.C. is also promising to deliver a tiger dam system — stackable orange tubes filled with water — that will encircle the market, and will set up a sandbagging station on the property for surrounding landowners.

“It gives you some sense of relief,” Calverley said.

Dave Campbell of the province’s River Forecast Centre said although most Island rivers were at record lows earlier this fall, heavy rains could change that quickly.

The centre will be watching the second rain system on Sunday closely, he said, to see how quickly major rivers like the Cowichan, Chemainus, Nanaimo and Puntledge fill and if any are in danger of spilling their banks.

“We are tracking the rainfall and the intensity [in real time],” said Campbell.

There is concern that natural flood plains around Island rivers are baked hard from months of drought, which could allow spilling river water to spread rapidly. However, Campbell said rains over the past couple of weeks have shown surrounding soils are absorbing rainwater. “There’s been no active runoff, so the soils are in good shape for continued absorption,” he said.

Adding to the stormy brew this week, Environment Canada is forecasting southeasterly winds ranging from 30 to 50 km/h and up to 70 km/h on Thursday and into the weekend, prompting a warning from B.C. Hydro that trees with drought-compromised root systems could fall on wires and cause outages.

Hydro said its meteorologists are predicting a greater likelihood of substantial outages this fall and winter because of those “wind-vulnerable” trees.

It said this year’s conditions are similar to those in 2015 and 2018, when storms following a drought caused significant power outages. While trees affected by drought won’t show immediate effects, it said, the lack of water affects small structural roots that provide trees with stability, making them more susceptible to wind of any speed.

With wet, stormy weather predicted for the Lower Mainland, Vancouver Island and parts of the B.C. coast, Emergency Management B.C. says it’s prepared to deploy four million sandbags to local governments to protect homes and public infrastructure from flooding, and sandbagging machines are already in place or are ready to move to areas prone to flooding.

More than 10 kilometres of gabions — wall-like structures filled with sand — and 32 kilometres of tiger dams are also at the ready.

The agency is also expanding the use of its Alert Ready warning system to broadcast imminent flooding threats.

The digital registration system for emergency support services has also been expanded to include direct payment to evacuees through Interac e-transfer.

dkloster@timescolonist.com

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