B.C.’s river watchdog is keeping a close eye on the Skeena/Nass drainage basin as snowpacks are well above average, a circumstance that may foretell of flooding to come.
“It’s something that we’re watching closely to see how that’s going to evolve over the next couple of months,” says Dave Campbell, head of the provincial River Forecast Centre, adding end of season snow-pack depth was reached in January.
It’s now two-thirds through the season and the amount of snow accumulation has climbed. The regional snowpack is now 139 per cent of normal, close to the winter of 2006-2007’s 153 per cent of normal, which contributed to the late spring 2007 flooding along the Skeena River, said Campbell.
He said snowfall amounts this year represent an increased flood risk, and that he and others are taking notice.
“For the Skeena Bulkley, we certainly are forecasting higher volumes of water (melting) than normal,” Campbell continued.
Flood risk is higher when the weather turns warm, quickly accelerating the snow melt period.
“I think at this point, it’s still dependent on what we get for weather,” Campbell said. “If we get normal or wetter than normal conditions, certainly that will increase the flood risk.”
The precipitation measuring station at the Northwest Regional Airport has broken a 31 year snow-pack record – 25 per cent more accumulated precipitation than the winter of 2006-2007.
But to understand flood risk, the bigger picture needs to be taken into account, Campbell said.
Data was drawn from 13 sampling locations that drain into the Skeena/Nass basin this month. Twelve are located at a higher altitude than the airport, which averages less snow year to year.
At the higher elevations, ranging from 460 metres to 1,540 metres above sea level, the snowpack ranges from just a quarter more than usual to twice as much to date averaging 139 per cent more than the norm.
“We do see very high snowpacks for this time of year in the region and for Terrace,” said Campbell. “It’s higher than we’ve seen historically.”
Aside from snowpack, which determines how much water is available to melt off, weather is a large factor when it comes to flooding.
The coming months will have to be moderately dry for snowpack to return to normal, said Campbell.
Also, temperatures determine how much snow melts, and how quickly.
Currently, a mild La Nina cycle is in play.
La Nina is brought about by cooler than normal sea surface temperatures in the Pacific, and last year a strong La Nina contributed to higher-than-normal snowpacks, a cool spring, and a delayed and prolonged snow melt season.
What that means, said Campbell, is that likely cooler wetter temperatures would contribute to snow accumulating for a longer time period before melting.
“That’s something to watch out for,” he said, adding that, it’s too soon to say anything for sure.
“Weather in May/June will play a big role,” Campbell said. “In terms of flood risk… a hot snap in the middle of May or excessively wet conditions might cause rapid melt of that snowpack.”
Now, no flood warnings have been issued for the Skeena/Nass area.