The 2021 Fraser River freshet – the spring thaw marking the shift from snowpack accumulation to snow melt in the upstream watersheds – is starting.
According to the B.C. River Forecast Centre, the overall Fraser snow basin index was at 116 per cent of normal on April 1, which was the same level as last year this time.
“The weather is a big factor when talking about peak flows on the Fraser River,” according to the April 20 update to Chilliwack council by city staffer Frank Van Nynatten, assistant manager of environmental services.
The update on the 2021 Fraser River Freshet was received by Chilliwack city council this week as routine freshet preparations get underway by City of Chilliwack, and in communities across the Fraser Valley.
Intense and prolonged rain during freshet, for example or sudden, hot temperatures can make the snow melt flow faster, and increase the risk of snow-melt flooding during freshet regardless of snowpack levels.
At this point the predicted peak discharge of flows is between 8,999 and 11,500 square metres per second at Hope, and “above average flows are expected for 2021,” according to the update. The other main indicator is watching water levels at the Mission gauge.
The hot weather that’s coming for example could have an effect upstream but the weather that could impact the peak level across the Fraser Valley is that of the Central Interior.
Snow pack levels can impact seasonal water supply and flood risk, and April 1 is the date when 95 per cent of annual B.C. snow pack is in typically place, with the transition to snow melt usually starting in most areas by mid-April.
The peak reached during freshet is always weather dependent and staff will be monitoring conditions and providing updates May to July.
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