Warmer climate creates engineering challenges

Posted: Friday, January 10, 2003

ANCHORAGE (AP) -- Alaska's warming climate is creating new challenges for state crews grappling with damage to road surfaces, bridges and channels.

Last summer, a 25-foot-deep muck hole near the Northway Junction of the Alaska Highway opened up when frozen ground dissolved under a culvert about 75 miles from the Canadian border.

State crews kept the sinkhole from consuming the highway, but not before the culvert had snapped off and silty water flushed away a 100-foot stretch of earth along the shoulder.

''This is the kind of thing we're facing in the field on a regular basis,'' said George Levasseur, Southcentral district manager for the Alaska Department of Transportation, during a conference this week on climate change at the University of Alaska Anchorage.

The presenters ranged from a leading atmospheric scientist to a road maintenance chief to the retired captain from a U.S. Coast Guard icebreaker. They described a world where it's getting warmer, wetter and more unpredictable.

The Arctic has warmed over the past few decades, with the most dramatic warming concentrated in the spring and winter, said John Walsh, a leading climate scientist and the president's professor at the International Arctic Research Center at the University of Alaska Fairbanks.

Sea ice is shrinking, with 2002 marking the smallest polar ice cap on record. Alaska glaciers have lost mass, contributing to about half of the measurable rise in world sea levels.

Overall average temperatures have risen 7 degrees to 15 degrees Fahrenheit, he said. The edge of Alaska's permafrost will slowly migrate north as much as 200 miles over the next century, Walsh said.

The potential impact is huge for Alaska. Permafrost can be found in 166 Alaska communities with nearly 90,000 residents, and underlies 1,700 miles of Alaska roads, according to Lawson Brigham, deputy executive director of the U.S. Arctic Research Commission and the coordinator of a federal Permafrost Task Force.

This year, Levasseur's crews had to rebuild about 45 miles of highway in hundreds of locations throughout the region. It cost $4.5 million.

''The whole Alaska Highway from Northway to the border is coming apart,'' he said. ''It's just exploding.''

At least 700 miles of the 800-mile trans-Alaska oil pipeline cross discontinuous or permanent permafrost.

While pipeline operators don't worry too much about the very cold permafrost north of the Brooks Range, they do monitor pipeline supports stuck in much warmer permafrost further to the south, said engineer J. David Norton, who works with Alyeska Pipeline Service Co.

Some 182 of 78,000 the T-shaped pipeline supports are under close scrutiny. Twenty-four have been replaced since 2000 when they became too unstable, Norton said.

The meltdown has dumped silt and gravel into rivers and creeks in the Copper River basin -- filling culverts, causing floods, undercutting bridges, shifting channels, Levasseur said.

The Copper River has been carrying 100,000 tons of gravel per day into the delta during peak flows -- almost double what it carried 10 years ago, Levasseur said.

The river has shifted. What was once a main channel under a large bridge is now a trickle, while the main stem is rushing through overflow channels further east.

''We've had to extend those bridges twice,'' Levasseur said.



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