Upcoming precipitation will determine flood potential
The snowpack on the mountains is at the top of the normal range for moisture this year but it is too early to predict the likelihood of flooding, says Alberta Environment.
“We are at the very top of the normal range for a couple locations,” said Colleen Walford, river flow forecaster with Alberta environment.
Flood danger will come down to short-range precipitation and not simply another heavy snowfall. Environment Canada’s three-month range forecast is for “above normal” levels but that is about risk rather than a definitive verdict, Walford explained.
It will depend of how much more snow comes as well as how much rain. At one particular spot, Sunshine Village, it could take another 12 cm of snow before pushing beyond the bounds of “normal”, said Walford.
Typically we will still accumulate (snow) all the way through to the middle of May and until the middle of June for all the snow to melt in a gradual process, depending on temperatures and sunshine, said Walford.
One of the ways the amount of snow is measured is by using snow pillows.
“A snow pillow is a physical installation; it’s like a big bladder filled with liquid, and as the snow falls it compresses the bladder and it can measure the amount of water in that snow. It’s based on weight,” she said.
Snow surveys are also done and this involves people out in the field taking vertical samples of snow. A metal rod is inserted to pull out a column of snow. It is called a survey because they are covering a number of points within an area and they then take the average of those readings, said Walford.
Last fall included a lot of rainfall. This is taken into account in determining the runoff this year, said Walford.
“If it’s wet (the ground) then you’re not using the snow melt to refill all those little pores in the soil,” said Walford. “They’re already full but it’s been quite variable this year.”
Alberta’s agriculture’s soil modelling is fluctuating from week to week depending on snowfall, said Walford.
Typically, the fall moisture will not be sustained for the next six-months, and this region can dry out fairly quickly, particularly if it is windy.
Last year, the snow melt began in April and that can help reduce the risk of flooding because the snow could melt before spring rains begin, said Walford. That in no way means it wont’t flood if the rain arrives after the snow has melted.
“In 2005, there was no snowpack and there was flooding,” said Walford. “The driver will be the rain at the end of the day.”
The next two months of snowfall will be a better indication of risk, she said.