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Yukon's Dawson City treading on thin ice
Toronto Globe and Mail


March 06, 2006

DAWSON CITY, Yukon - This is a town built on ice, which is a real concern to Norm Carlson, who runs Dawson City's public works.

He has seen the early warning signs of climate change: massive spruce beetle infestations, extreme wildfire and fast spring floods.

Next up: melting permafrost.

For this outpost of 1,500 people, that could lead to the destabilization of the town's dirt roads, buried sewers and water lines, which are encased in naturally occurring ice or frozen muck just below the surface.




"If the permafrost fails here, everything is going to snap," Carlson said. "It just can't take that kind of movement. Roads would melt, the whole town would sink. We would lose all our infrastructure wherever there is ice in the ground. It would be soup."

There are early signs of a problem. In February, one section of a water line dropped at a joint, causing a large tear. The problem was discovered when water filled, then froze, a manhole nearly a block away. The damage was repaired at a cost of $20,000.

Crews are constantly on the lookout for sinking ground and frozen manholes. The longer the water runs underground unchecked, the more it melts the ice, further destabilizing the infrastructure.

"Once you have a break in Dawson, it saturates all the ground around it," Carlson said. "If that's a permafrost area, it stays saturated and you have seriously weakened the infrastructure around the whole area."

Chris Burn, a geography professor at Carleton University in Ottawa, has spent more than 20 years studying the effects of climate change on permafrost in the North, including central Yukon.

Warmer air temperatures heat the ground and cause a warming of the active permafrost layer, he said. In Dawson City, the active layer is filled with natural groundwater that freezes in winter and runs in summer. This freeze-thaw cycle causes the ground to heave during fall and spring.

A greater than average snowfall, which the town has experienced the past three winters, insulates the earth and prevents summer heat from escaping into the air, further warming the ground.

The warming of the active layer, because of climate change and human activity, will destabilize the ground and any infrastructure that it supports, Burn explained.

"In Dawson there is quite a lot of ice in the ground. It's what we call ice lenses. When those thaw out, we lose volume in the ground. There is nothing to hold the structure together."

Burn has been stationed in Mayo, a village east of Dawson City, since he began his investigations in the 1980s. In the village he has studied the soil and measured the warming temperatures of the deep and active permafrost layers.

In the past three years, the summer temperature of Mayo's soil has jumped to 6.5 degrees from 5.5.

That is a dramatic increase, Burn said, but it will not happen in Dawson so quickly because the ground will warm only after the ice disappears, and ice is difficult to melt.

Mayo is different than Dawson City because the active permafrost layer melted quickly when the town site was created in 1902. This now allows for consistency in building infrastructure projects because the ground moves little in the freeze-thaw cycle.

Dawson City is not so lucky, Burn said.

"The difficulty in Dawson is that hasn't actually happened yet. It's still got quite a long way to go before the active permafrost is sufficiently deep down that it doesn't affect what's happening near the surface. In the long run, it is good that things are thawing out. At some point, things are going to become stable.

"In the time scale of centuries, it's short-term pain for long-term gain. In the time scale (residents) are looking at, it's a pain in the neck."

That is small consolation for Carlson, the public-works manager. The town's water and sewer maintenance budget for 2006 is set at $1 million, an increase of $340,000 from 2005.

Some of that budget will go toward replacing water-line joints with stronger seals that can endure the strain of the shifting earth. Other funding will go toward a continual upgrade of sewer pipe that is stronger and more flexible than what was installed in 1980. Most of this pipe was crushed by the shifting ground a decade after it was installed, and is slowly being replaced.

Spending thousands of dollars to dig up the street and fix a leaky water line or crushed sewer pipe is a short-term approach to dealing with a failing system, Carlson said, so the municipality must continue to adopt long-term approaches to dealing with a shifting environment.

"Engineers would come up here today and design something, and I would have comments. They would design typical southern construction. Northern construction is different. We have experience in that type of thing. I think in 50-year terms because I know the difficulties in trying to fix these types of things."


Distributed to subscribers for publication by Scripps Howard News Service,

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