Spring weather and snowpack levels are the main factors in determining seasonal flood risk on the Fraser River.
City of Chilliwack officials are watching both very closely now, as city crews conduct their annual prep work for spring freshet.
“As our province continues to feel the impacts of last November’s storms, people are understandably more focused on freshet this year,” said Mayor Ken Popove. “I would like to assure our residents that the city’s annual preparations are underway, our dikes are inspected regularly, and we are prepared for this spring.”
The overall Fraser basin snowpack average was sitting at 102 per cent of normal as of April 1, said Frank van Nynatten, the city’s assistant manager of environmental services, in presenting the freshet update to council on May 3.
“Weather patterns during the snow melt play a significant role in whether or not flooding occurs,” van Nynatten said.
Intense or prolonged rainfall, and extreme temperatures like a heat wave, can lead to flooding, even for areas with near normal snowpack.
At this point, water levels at the Mission gauge are forecast to peak at 5.3 metres for 2022 freshet, which would be “slightly above average” flows.
To compare peak freshet reached 5.5 metres at Mission in 2021, and 6.4 metres in 2012, which was a 1:20 event. The flood of 1948 saw 7.5 metres.
Cooler weather in late spring, like what we’ve seen, can also delay snow melt and lead to increased seasonal flood risk.
“Current weather forecast is predicting cool temperatures for the next few weeks,” the city staffer said. “So an extreme peak is still possible.”
An example of this was the flood of 1948, which devastated the region despite a near normal snow pack in early spring.
Millions have been spent upgrading Chilliwack’s dike system in recent years.
The city’s flood response plans for the Fraser and Vedder Rivers dictate that staff keep an eye on the river forecasts, including 10-day flow and water level forecasts, and take further action as necessary to keep the public safe.
Mowing and inspecting the dikes are part of the prep. City crews will also inspect the city’s pumps, floodboxes, and gates.
“The city is prepared for freshet, and now is a great time for residents to make sure they are prepared, too,” said Popove. “Reviewing your emergency plan with your household and knowing where to find credible information now can really help reduce some of the stress if there is an emergency later.”
“Freshet” is the term describing snow-melt runoff that leads to increased water levels on the Fraser and swollen creeks, generally from May to July.
Information about how to create an emergency plan, emergency kit, and grab-and-go bags is available on the City’s website at chilliwack.com/prepared or preparedbc.ca. For more information about flood protection in Chilliwack, visit chilliwack.com/FloodProtection or call 604-793-2757.
READ MORE: 2021 snowpack was at 116 per cent of normal as of April 1
READ MORE: 2018 freshet evoked the flood of 1948 for some
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