British Columbia’s River Forecast Centre has issued an upgraded flood warning for the Sumas River, a tributary of the Fraser River east of Vancouver, as the latest round of atmospheric rivers deluge the province’s South Coast.
An updated bulletin says flows in the Sumas River are not anticipated to pose a hazard for flooding into Sumas Prairie, an area hit hard by rainstorms and flooding that swamped much of southwestern B.C. in November, 2021, washing away bridges, inundating farmland, and spurring landslides that killed five people.
But in neighbouring Washington State, the bulletin says high flows on the Nooksack River reached “local flood stage” on Sunday.
It says “spillover” into the Sumas River watershed had been observed near the community of Everson, Wash., about 20 kilometres south of Abbotsford, B.C.
The bulletin says the spillover was expected to be “short-lived” as upstream areas of the Nooksack have already reached peak levels and started to recede.
The River Forecast Centre has also added a high streamflow advisory for the North Coast, including tributaries around Kitimat and Prince Rupert.
Environment Canada meanwhile added a rainfall warning for Kitimat, saying the community could receive up to 75 millimetres of rain by Tuesday morning.
A wind warning also spans Prince Rupert and Haida Gwaii, where the weather office says gusts could reach speeds of 110 kilometres per hour before easing Monday.
The River Forecast Centre says atmospheric rivers delivered between 50 and 160 millimetres of rain to the province’s South Coast between Friday and Sunday, and forecasting suggests two more systems will arrive by Tuesday.
A flood watch remains in effect for Vancouver Island, the Sunshine Coast, the North Shore mountains, Howe Sound, the Sea-to-Sky region and parts of the Fraser Valley.
A lower-level streamflow advisory is also in effect for the Central Coast.
Sunday’s update says rivers with potential for flooding on the island include the Gold, Salmon, Somass, Englishman, Qualicum, Chemainus and Cowichan rivers.
On the mainland, it says rivers with potential for high flows and flooding include the Stawamus, Squamish, Mamquam and Cheakamus rivers, as well as tributaries around the North Shore mountains, the Fraser Valley and the Sunshine Coast.
An Environment Canada bulletin says snowmelt from above-seasonal temperatures is adding to the potential for flooding and landslides throughout the South Coast.
The heaviest rain is expected on Monday, it says, but the rainstorms could last until the middle of the week.
The weather office says the rains combined with mountain snowmelt raises the risk of landslides in “vulnerable areas” as water falls on already-saturated surfaces.