Flood risks for Big Eddy area subside

Posted: Thursday, January 03, 2008

The risk of flooding along the Big Eddy area of the Kenai River has subsided thanks to stable temperatures keeping the formation of ice jams at bay. The National Weather Service lifted a small stream flood advisory for the area last week and hydrologists say if temperatures stay above 10 degrees or the river freezes over, Big Eddy residents can expect flooding to be minimal.

"Temperatures have remained well above frazil ice development standards," said Jim Coe, a hydrologist for the Alaska-Pacific River Forecast Center.

Frazil ice develops from exposure to prolonged periods of cold. Ice crystals form in moving water and back the river up, particularly at Big Eddy, which has a flat gradient and is low-lying.

Coe said when the ice grounded at Big Eddy, the river overflowed its bank just enough to get within inches of the roads. But after speaking with Scott Walden, the emergency manager for the Kenai Peninsula Borough, who wasn't concerned about further flooding, Coe said the weather service decided to lift the advisory. There are also frazil ice accumulation models based on temperature that can give forecasters a heads up as to what's happening on the Kenai Peninsula, but they're not foolproof, Coe said.

"Once certain thresholds are reached we start communicating with emergency management down there," he said. "That's what happened prior to Christmas and we finally let (the advisory) expire on (Dec. 26)."

Temperatures have to sink to 10 degrees or less for frazil ice to form, Coe said. But if the river freezes up, even if it were to get that cold, the ice would insulate the moving water underneath it, keeping frazil ice from forming. Once that happens, it would take a huge event, like the release of a glacial dam, to make the river overflow its banks.

Water has either frozen up or subsided on Joe Hanes' driveway. Subzero temperatures, ice jams and inadequate culverts backed up approximately a foot of water onto Hanes driveway at Salmon Run Acres off Eddy Lane near Soldotna prior to Christmas. He, too, doesn't expect any further flooding unless 2007's ice jam event decides to repeat itself this year.

"It's all locked up there for the winter now," he said. "There's still some slight fluctuation in the water around the edges, but it's pretty much found its way underneath the ice. Unless something drastic happens, we're in good shape."

Coe said even though flooding conditions have currently subsided, he wouldn't rule out any further flooding at the Big Eddy area or other portions of the Kenai River.

"If the river gets frozen over then there's less of a problem of (flooding). You're not supercooling the water from the air, it's insulated by ice cover," he said. "The winter's long from over, I wouldn't make any bets that it couldn't (happen)."

Jessica Cejnar can be reached at jessica.cejnar@peninsulaclarion.com.

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