Too early to worry about flooding, engineer says

As flood waters sweep through B.C. and Eastern Canada, Alberta forecasters are hopeful a heavy snowpack will gradually melt before the province’s flood season begins in earnest next month.

Four years removed from devastating floods that ravaged southern Alberta, the Rocky Mountain snowpack is currently measuring 58 mm more than in 2013, said Colleen Walford, a river forecast engineer with Alberta Environment.

But while the abundance of snow in the mountains may create some tensions for those downstream in the Bow River basin, Walford noted any significant flooding is primarily the result of extended and intense periods of rainfall combined with heavy snow melt in higher elevations.

“The snow surveys we did at the beginning of May are above average for us. But if you look at 2014, nothing really happened and the snowpack was 17 mm more than in 2013,” she said.

“We’ve just had a good nine days of melt — Sunshine Ski Hill went down 80 mm over that period. It would be ideal if it keeps melting the snowpack at this rate.”

Due to the melt, rivers in the basin below the mountains have swelled, however Walford said the water is still below typical levels.

The 2013 flood that devastated communities downstream of the Bow River was caused by a number of factors that occurred at just the right time. Three days of unrelenting precipitation between June 19 and 21 combined with a deep mountain snowpack left soil saturated, sending a rush of concentrated water downstream to unsuspecting communities.

The disaster caused more than $5 billion in economic damage and forced the evacuation of more than 100,000 people.

Walford warned any long-range forecasting of conditions favourable to flooding is always a tricky business.

“What really makes a big difference is a big low-pressure system, but those don’t usually come into the Bow corridor until June,” she said. “The long-range forecast is saying we’ll have normal precipitation, but you always have to take that with a grain of salt this far out.”

Forecasters have taken some lessons from the 2013 deluge, Walford said, when it comes to getting advance warning of looming floods. She said the province has set up rainfall alarms in the mountains to alert them of intense precipitation that might speed snow melt, along with threshold alarms in the rivers that warn of dangerously rising water levels. “We’re also more robust in how we deal with water modelling data,” Walford said.