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Snow Measured to Assess Flood Risk

March 11, 2009 - AUGUSTA - Using a hollow metal pipe and a weight scale, Robert A. Johnston can help forecast spring floods about as accurately as meteorologists forecast the weather.


"It's an educated guessing game," said Johnston, a senior geologist with the Maine Geological Survey, as he and others gave a snow-measuring demonstration Thursday in Augusta.


"The more data we get, the better predictions we get. We have hard data from over 100 sites, so we're getting a better snapshot of what conditions are like," Johnston said.


His sampling pipe, known as a snow tube, is pushed vertically into the snowpack to measure depth by reading the ruler gauge on the outer side. The core of snow packed inside is weighed to determine water content in inches.


Measuring the depth of Maine's snowpack and its water content at least six times each winter from mid-January until the last snow vanishes at more than 100 statewide sampling sites, then averaging the totals, can determine snowpack density - the water equivalent in inches divided by snowpack depth in inches. The higher the water content, the greater potential there is for spring flooding during snowmelt.


The method worked in April 2008.


"With the Fort Kent flood, we knew it was going to happen within 24 hours," said Maine Geological Survey Director Robert G. Marvinney. "Twenty-four hours was enough time for people there to get their cars out and get stuff up to the second floor."


That flood occurred when nonstop rain for two days combined with snowmelt to overrun the town, forcing people to flee to higher ground.


This winter's snowpack contains much less water content than last year's, Marvinney said.


"Flooding (this spring) is not just going to happen with snowmelt alone," he said.


A lot will depend on the weather in the next month, Johnston said. "Last year, it looked like there was a real flooding potential with 12 inches or more of water in the snowpack and it all built up to that potential. But I think this spring, we're unlikely to get to that condition. We had a lot of fluffy, light snow, which has less water content."

As of this week, Maine's snowpack depth ranges from 24 to 44 inches, with a water content ranging from 5 to 9 inches. Last April, most of Aroostook County had more than a foot of water in the snowpack, Marvinney said.


The geologists said they learned Thursday morning that an 18-day forecast from the National Weather Service calls for fairly cold temperatures.


"So, there's not a chance that (the snowpack) will melt fairly quickly," Marvinney said.


Geologist Jim Caldwell agreed.


"This snowpack itself probably won't cause flooding as it melts, but if we have rain with it, that's when we worry," he said. "Also, if we carry this snowpack after March 10, then you're getting into a bad situation, because April is warmer and wetter."

By Terry Karkos , Staff Writer, Sun Journal,
Friday, March 6, 2009


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