Floodplain areas of the Lower Mainland are shown in white with standard dikes marked with red lines.

Fraser flood risk elevated due to snowpack

River forecasters say much depends on spring weather, speed of melt

There’s a higher risk of flooding on the lower Fraser River this year because of heavier-than-usual snowpacks across central and northern B.C. that have been slow to melt due to a cold spring.

All the major tributary basins that feed the Fraser have above average snowpacks, and the entire watershed holds 31 per cent more snow than usual, according to the latest readings from B.C.’s River Forecast Centre.

“That is about the fifth or sixth highest reading we’ve seen for the Fraser for this time of year,” said centre head Dave Campbell. “It’s something we see about once every 10 or 12 years.”

He said this is the second straight year of a La Nina weather pattern, which tends to cause cool and wet weather in late winter and spring, bolstering snowpacks.

Some parts of the watershed are actually at record snow levels – the Nechako is 65 per cent above normal and the upper Fraser basin is 52 per cent higher than usual. Those two basins supply a third of the flow that comes to the lower Fraser Valley.

Whether high water actually threatens to top Fraser River dikes will depend heavily on spring weather patterns in May and June and how quickly all that snow upcountry melts and flows downstream.

Campbell said a worst case scenario would be continued cool weather for several weeks followed by a heat wave, especially if heavy rains are added to the mix.

The best scenario would be seasonal temperatures and dry weather for the rest of the spring.

So far, he said, the long-term forecasts suggest B.C. is in for dry but hotter than normal conditions later in the spring.