Arrival of hot, summer weather replaces rain as B.C.’s chief flood risk

Click to play video: 'Temperatures and water levels set to rise this weekend along with certain risks' Temperatures and water levels set to rise this weekend along with certain risks
After an unseasonably cool, wet spring, many British Columbians are welcoming a weekend with the first significant heat of the year. But as our Paul Johnson shows us, it does come with some risks. – Jun 24, 2022

A number of waterways around British Columbia remain at risk of flooding as warm weather, rather than heavy rain, becomes the chief concern.

The arrival of a ridge of high pressure has prompted Environment Canada to issue special weather statements about the first significant heat of the year for most of the province, with temperatures forecast to be five to 10 degrees above seasonal daytime highs.

Read more: Shuswap Lake approaching 2018 water level, but expected to peak soon: Regional District

“This is not record breaking like we saw during the heat dome of 2021, but it is covering most of the South Coast, the southwest Interior and the central Interior all the way up into Dease Lake area,” said Armel Castellan, warning preparedness meteorologist with Environment Canada.

Click to play video: 'B.C. flood watch: changing weather concerns' B.C. flood watch: changing weather concerns
B.C. flood watch: changing weather concerns – Jun 22, 2022

The end of persistent rain has also prompted the BC River Forecast Centre to lift a flood warning for Blue River. A flood warning for the Quesnel River, however, remained in effect, with water levels forecast to hit a 20-year flow over the weekend.

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As of Friday, flood watches remained in effect for the North Thompson, South Thompson, Thompson, Shuswap and Liard rivers, along with northeastern B.C.

High streamflow advisories were in effect for the Peace Region, northwestern B.C., the Upper and Lower Fraser River, Swift River, Nechacko River, the Illecillewaet River, the Upper Columbia River, the Kootenay River and the Nicola River.

The City of Chilliwack issued an evacuation alert Friday afternoon for seven properties outside the city’s dike system in the Carey Point area.

Dave Campbell, head of the River Forecast Centre said the province faces three primary risks in the coming week.

Read more: Rain, impending heat wave prompt warning and raise flood potential in B.C.

The Fraser River around Prince George and the Thompson River near Kamloops are both still at risk from the “pulse of water” produced by heavy rain over the past week, he said.

“These are fairly modest rises above what we’ve got in terms of the current levels, but it is representing the highest flow levels we have seen this year,” he said.

That risk, however, is being replaced by the potential for increased runoff from high-elevation snowmelt in the coming days, amid the hotter temperatures.

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Click to play video: '‘It will continue rising for at least another week,’ emergency officials watching rising water levels in Okanagan Lake' ‘It will continue rising for at least another week,’ emergency officials watching rising water levels in Okanagan Lake
‘It will continue rising for at least another week,’ emergency officials watching rising water levels in Okanagan Lake – Jun 20, 2022

While most mid-elevation sites are now snow-free, he said high elevation sites have only seen about half to three-quarters of their snow melt.

Campbell said runoff from those snowfields had the potential to generate periods of high flow in large rivers across the province.

“We do anticipate that the impact of this accelerated snowmelt will be fairly measured, in terms of river levels,” he said.

“Though there’s certainly the possibility to see some gradual rising as we go through the latter part of the weekend, particularly in those higher elevation sites, including the upper Fraser River, the South Thompson River as well as the main stem of the Thompson.”

Read more: Delayed snowmelt, rain, impending heat make flood predictions challenging in B.C.

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Campbell said a potential dose of heavy precipitation arriving on the central and southern coast of B.C. around Tuesday next week could also raise the risk of flooding.

“With rivers high, coming into that period, there’s certainly is increased vulnerability,” he said.

Localized flooding has already been reported along some areas of Shuswap Lake, but officials predict levels should peak this weekend, avoiding severe flooding, while the City of Abbotsford says the Lower Fraser River will crest within six to nine days.

A post on the city’s website says levels will stay high for several days once the peak is reached and “residents living in areas along the Matsqui Dyke and Glen Valley Areas may experience pooling of water or seepage.”

An evacuation alert issued two weeks ago by the District of Kent, just east of Abbotsford, is still in effect for properties at the mouth of the Harrison River where it joins the Fraser River.

But drier conditions have allowed the District of Sicamous to lift the latest evacuation alert for 27 properties in a mobile home park at the base of a slope considered extremely likely to slide sometime in the next two years.

— with files from the Canadian Press

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