With flood waters rising across B.C.’s Southern Interior, all eyes in the Lower Mainland have turned to the Fraser River.
The River Forecast Centre has issued a 10-day high streamflow advisory for the Fraser, warning that water levels could reach 6.5 metres by late next week at the Mission Gauge, and possibly higher after that.
WATCH: Fraser Valley flood watch
That’s already prompted a pair of evacuation alerts to about 20 properties in low-lying areas of Chilliwack not protected by the city’s dike system. Mayor Sharon Gaetz said officials are watching the water levels closely.
Gaetz said the city has updated its dike system since 2012, and has its pump system standing by.
WATCH: Flood waters rise in Grand Forks
“We’re watching the weather very closely. If it gets too hot, or if there is too much rain, then there’s the possibility that the river will rise more rapidly than we had anticipated,” said Gaetz.
“We have a full team going out and checking the dikes to make sure that there are no vulnerabilities in the dike, they do that every single day.”
Gaetz is also warning the public to stay clear from the Fraser’s banks where possible, as they may be unstable.
READ MORE: Lower Mainland vulnerable to significant flooding, costing billions in losses: study
Public Safety Minister Mike Farnworth said the Emergency Management Centre in Surrey has also been activated to help coordinate the provincial response to flooding.
And he said while there is currently no risk of major flooding in the Lower Mainland, he’s warning the public not to be complacent.
“People need to be prepared, they need to understand this is not an Interior problem. The Fraser Valley and Lower Mainland are at risk, particularly low-lying areas.”
Back in 2012, the flood season saw dozens of evacuation alerts issued across the Fraser Valley, along with several evacuation orders. The 1972 flood event wreaked an estimated $10 million in damage across the region.
A 2016 study from the Fraser Basin Council warned that a worst-case flood scenario for the Lower Mainland could be the most costly natural disaster in Canadian history.
In that extreme scenario, in which each of the flood-protected dikes in the region failed, the study estimated in a $20 to $23-billion loss. However, the study also warned that some Lower Mainland dikes built in the 1970s and 1980s were not designed for today’s climate change effects on flood risk.
Watching the Fraser
By 10 a.m. on Friday, Fraser River levels on at the Mission Gauge had reached 4.9 metres.
That measuring point is key for municipalities and emergency planners around the region, explained David Blain, Chilliwack’s director of planning and engineering.
“You often see us as well as other communities establish our notices based on the Mission Gauge because that’s where we have the longest period of record, so it gives us a good sense,” he said.
“We know what happened there in 1948 and before. So that’s why everything is related to the Mission Gauge. We know water levels all up and down the river as they relate to the Mission Gauge.”
According to the Fraser River Freshet Stage and Response, a level of 5.5 metres at the guage is considered “full bank” conditions, where the water has risen to the natural banks but not spilled into the floodplain.
At six metres, there is flooding in unprotected areas outside the city’s dike system, and over seven metres, it has pushed into the floodplain adjacent to the dikes, causing “extensive flooding of the unprotected areas outside of the city’s diking system.”
At over eight metres, the river has easily topped dikes.
That’s happened twice in the last century and a half, explained Blain — and has formed the basis for modern dike design.
WATCH: Archive footage of the widespread flooding in B.C. In 1948
“The other major event was in 1948. And there were dikes breached in the lower mainland, including here in Chilliwack. So there was some significant damage.”
In that case, water levels reached around eight metres, and while it didn’t top the dikes, it burst through at Agassiz, Matsqui, Cannor and Semiault, according to the Chilliwack Achives.
The flood forced evacuations from Greendale and Herrling Island, cut the CNR railway connection with Eastern Canada, forced a response from the Canadian Army, and killed thousands of livestock.
Following that flood, all dikes were widened and heightened with gravel and silt, and have since been upgraded to hold against 1894-level floods, according to the archives.
The City of Mission has circulated a notice warning people to know their risks and have an emergency plan in place.
They also recommended that people speak with their neighbours and insurance broker, and to watch water levels and be ready to act.
- With files from Janet Brown and Paula Baker