High snowpacks around B.C. are stirring concerns about the high flood risk in many parts of the province – including communities in the Fraser Valley.
Across the Fraser River basin, snowpacks remain 20 to 50 per cent above average. The aggregate snowpack upstream of the Lower Mainland is at its highest level in decades.
It has Abbotsford Mayor Henry Braun watching the situation carefully and hoping the city doesn’t have another emergency to deal with in the weeks and months to come.
“I don’t like what I see up there,” he said.
Jonathan Boyd, a hydrologist with the River Forecast Centre, said the combined index for all upstream snowpacks is the highest it has been since 1999. Records don’t exist before that point.
“We’re not in a great situation in terms of the snowpack,” Boyd said.
It’s not time to panic. But it is reason to worry.
“There’s lots of variables and in order for a record flood to happen, you have to have everything happen in the worst case scenario. But right now, we do know that the snowpack is high enough that it does have that capacity to be there,” Boyd said. “Everyone should be aware the risk is there.
“If the perfect storm for climate and weather conditions occurs, that there could be a risk of very high flows for the lower Fraser Valley,” Boyd said.
The best thing that could happen would be an extended period of quite warm weather. But although sun has blared down for more than a week, Boyd noted that temperatures haven’t been particularly high, and the nights have been chilly.
That means the snow hasn’t been melting much. And the longer it remains in the mountains, the danger increases as the days lengthen and the likelihood of a heat wave rises. The one good thing, Boyd says, is that more snow hasn’t fallen recently to add to that base.
Boyd said the biggest danger scenario includes a sustained run of cool temperatures, followed by a sudden and extended hot spell in May.
“That’s what happened in 1948 when the Lower Fraser flooded considerably,” he said.
Dikes have been beefed up since then, but remain below provincial standards.
One additional domino could increase the severity of any flood.
“What didn’t happen in 1948 is there was no rain. The ultimate variable is if you get a big rain storm falling within the Fraser as it’s peaking.”
If there’s good news, it’s that any flood won’t come completely out of the blue.
Weather forecasters will be able to predict a long spell of hot weather, and preparation can take place as a heat wave is ongoing, in preparation of what is to come. Prince George and Kamloops would also be hit days before the Fraser peaks in the Lower Mainland, providing a clear warning to officials here.
But one other wild card is the health and stability of the dikes that protect thousands of homes and billions of dollars worth of infrastructure in the Fraser Valley. If those dikes hold, the damage from extremely high waters can be minimized. But if they fail, as they did in 1948, all bets would be off.
For Braun, the flood threat is a nagging worry at a time when the city and other municipalities are scrambling to adjust to the implications – both financial and logistical – of COVID-19. Braun has said the city has enough money in reserves to cover the financial implications of tax shortfalls.
But, he noted, “That $43 million could disappear very quickly if a dike goes.”
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