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Glacier dam lake holds flood risk

Posted: Tuesday, July 31, 2001

Attention low-ground, Kenai riverfront property owners: Mother Nature may be plotting mischief.

High in the mountains northeast of Seward, the Snow Glacier Dammed Lake is filling. Trickles of water in the remote highlands and deep beneath the nearby glacier are building toward a periodic glacial outburst flood.

"It is almost guaranteed to go at some point in time this year," said Larry Rundquist, a hydrologist with the National Weather Service's Alaska River Forecast Center in Anchorage.

The lake is due to rupture soon, and people involved in flood forecasting and emergency preparations are concerned.

Friday, Kenai Peninsula Borough officials chartered a plane to fly over the lake and other areas of flooding concern and check out their status. Rep. Ken Lancaster, R-Soldotna; borough Mayor Dale Bagley; borough Emergency Management Coordinator Jan Henry; and Rundquist were on board.

Flying over the lake has been a borough priority since last summer, Henry said, and more so with conditions this summer.

He described the borough's monitoring of the glacier dam lake as "watchfully cautious."

National Weather Service personnel previously flew over the lake June 28. Since that time, the water has risen 20 feet and is now 10 feet below the level it was when the lake last burst out in 1998.

Rundquist predicted the lake will start draining in August or September, possibly as late as October.

"It is too early to say," he said.

"It could be releasing as we speak. There are too many unknowns about the system up there."

What the release will mean for people along the Snow and Kenai river systems depends on many unpredictable variables. But because the Kenai River is unusually high this summer, the risk is elevated.

The borough emergency office would be more worried about heavy, prolonged rains than the glacier dam lake, but it is a cause for concern, Henry said.

"We are not at flood stage, but we are not too far beneath it. Who knows what would happen if it went today," he said.

Rundquist agreed.

"If it's already high, it could certainly cause problems," he said.

Rundquist said the lake contains a lot of water. Although its surface area is small, it is deep. He estimated it contains more than enough water to flood 100,000 acres to the depth of one foot.

When the Skilak Glacier Dammed Lake released in 1999, it raised river levels downstream more than three feet, he said.

"It really depends on the conditions right at the time of release," he said.

Rainfall and runoff are the biggest variables. Heavy rain causes upward spikes in river volume, and the annual rainy season for the peninsula is just beginning. Runoff from heavy snow pack caused the high water this summer, and plenty of snow remains in the Snow River area. Glacial melt usually peaks about this time of year, Rundquist said.

How those factors will combine for the rest of the summer is the big question.

As the weather cools, the runoff will diminish and so will the danger from the glacier dam lake, he said.

Although the risk of high water is real, homeowners and emergency workers should have plenty of time to plan. Such a flood would be, to some extent, a disaster in slow motion.

When the outburst happens, it begins gradually.

Water from the lake flows into the Snow River. A gauge on the river monitors the water level. When the Snow River goes up, it takes several days for the same pulse of water to travel as far as Soldotna.

"There is usually pretty reasonable advance notice downstream," he said.

Among those particularly interested in advance notice is a Herndon and Thompson road construction crew working on the Seward Highway upgrade by Grouse Creek north of Seward.

The contractor has been parking equipment on a gravel pad on the bank of the Snow River, and people have expressed concern that a flood could sweep heavy equipment and contaminants such as fuel and asphalt into the river.

Fred Thompson, the project's supervisor, said the company has been as anxious as anyone to get the construction camp away from the river.

Herndon and Thompson still has a crusher next to the river, but the other equipment has been moved to higher ground, and the crew has a plan for evacuating fuel and building berms if the water rises. The company is due to finish paving within the next few days.

"In a week we hope to be moving out of there," Thompson said.

Lancaster, who represents peninsula communities along the river drainage from Primrose to Soldotna noted that Snow Glacier Dam Lake is not the only threat lurking in the mountains.

Rundquist told him Cooper Lake could be a bigger danger if a major earthquake or other disaster destroys the manmade dam there.

"It's another thing to worry about," Lancaster said. "Hopefully, it's all right for at least a few years."



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