Chena River sees 'classic' breakup

Posted: Friday, May 03, 2002

FAIRBANKS (AP) -- The Chena River was littered with huge chunks of ice Thursday after what hydrologists called a ''classic'' breakup.

The 2 1/2-foot-thick blanket of ice that covered the river was ripped off and broken to pieces by a surge of water produced by the almost 3 inches of rain and 8 inches of snow that fell on Fairbanks in the last week.

''All that water finally made its way into the system brought the river up before the ice melted,'' said Bob Burrows, a hydrologist for the U.S. Geological Survey in Fairbanks.

''Ice is buoyant and when you have enough water underneath to lift it up it starts to break up. That's what a real breakup is.'' he said. ''This doesn't happen very often on the Chena River anymore.''

Icebergs ranging in size from pizzas to parking spaces floated down the river most of the day, creating a series of ice jams on the lower section of the river that caused water to back up in several spots before the jams worked their way down the river.

In a normal spring, warm temperatures tend to rot the ice and it dissolves, rather than breaking up, Burrows said. By the time the current is strong enough to move the ice it has turned to mush.

But this year, with April winding up as one of the coldest on record, the ice was still more than two feet thick when it broke up.

Hydrologists don't know what will happen when all the ice hits the Tanana River, which is still frozen more than three feet thick. There's a good chance the surge of water and ice could hasten breakup on the Tanana River, Burrows said.

Both the Chena and Salcha rivers are pouring a high volume of water into the Tanana River, he noted.

''The Tanana is going to start breaking up in a matter of days,'' he said. It's doubtful an ice jam at the mouth of the Chena River will back water up enough to cause any flooding, unless it comes as a result of the water table rising, Burrows said. The Tanana River is big enough to handle the flow coming from the Chena, he said.

''It's unlikely the Tanana is going to create much of a backwater situation unless an ice jam forms on the Tanana,'' Burrows said.

What happens to water levels in local rivers over the next two or three weeks will depend on the temperature. There is still a considerable snow pack in the hills around Fairbanks, following the second-snowiest April on record.

While Fairbanks received more than 15 inches of snow, three times that fell in the hills in some areas. If the temperature warms up too fast, all that water could come pouring into Tanana Valley rivers.

Fairbanks received more snow on Thursday morning when 1.8 inches of snow was recorded at the Fairbanks International Airport, doubling the previous record for a May 2 snowfall. The old record was nine-tenths of an inch set in 1945.

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