RogerRabbit
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Joined: 05 Sep 2004
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Location: Oregon
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 Posted: Sun Apr 24, 2005 3:48 pm Post subject: nterior could undergo dynamic breakup this spring |
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http://hosted.ap.org/dynamic/stories/A/AK_SPRING_BREAKUP_AKOL-?SITE=AKFAI&SECTION=HOME
| Quote: | FAIRBANKS (AP) -- The National Weather Service is warning that conditions are right this spring for a dynamic breakup in Alaska's Interior.
Computers are telling meteorologists and hydrologists that breakup this year could involve flooding, ice jams and significant erosion in fire-ravaged areas.
Record-setting snow depths and water-content measurements have hydrologists warning of the potential for spring floods along several major Interior rivers.
"They should be getting prepared," said Scott Lindsey, a hydrologist with the National Weather Service's Alaska-Pacific River Forecast Center. "There is a potential for what the villages call 'spring flooding,' when the snowmelt ends up causing flooding after the actual breakup."
A significant amount of water, most of it locked away in ice and snow, sits in the drainages of several Interior rivers, including the Yukon, Koyukuk and even the Chena. The same is true for much of the huge Susitna River drainage in Southcentral.
Scientists describe the two kinds of breakups as "thermal" and "dynamic."
A thermal breakup, as described by Larry Hinzman of the University of Alaska Fairbanks, occurs when temperatures warm gradually over several weeks, allowing the river to thaw slowly as the ice rots.
The Interior this spring is more likely to undergo a dynamic breakup. That occurs when temperatures are relatively cool - such as experienced in the Interior over the last month - and then become very warm.
Conditions like those on Friday, with the temperature hovering at or above freezing at night, then soaring as high as 60 under increasingly sunny skies, are just right for a dynamic breakup. String together a week of conditions like that and water is streaming over frozen ground into rivers that are still locked in ice.
Rick McClure, who oversees the cooperative snow survey project for the Natural Resource Conservation Service, said hydrologists are able to predict the amount of water locked in a particular drainage.
The numbers coming out of their formulas are striking. For instance, the "volume flow forecast" for the Yukon River around Stevens Village is 116 percent of normal for April through July, McClure said. That means enough water will flow by the village to cover 48.2 million acres of land with 1 foot of water, a measurement hydrologists call acre-feet.
"Forty-eight million acres is about the size of South Dakota," McClure said.
McClure said some of the most impressive measurements came along the Yukon River near the Dalton Highway crossing, where water content was measured at 180 to 190 percent above normal, and in the White Mountains, where water content was 150 percent.
The Chena River basin also has significant water content, according to John Schaake of the Chena River Lakes Flood Control Project. Schaake said there is enough water contained in snow and ice to cover the basin to a depth of 6 1/2 inches. |
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