The Crested Butte News Serving the Gunnison Valley since 1999
“It’s very unusual to have an ice run in sustained cold periods.”
by Alissa Johnson
At a recent meeting of the Taylor River User Group there was over an hour of discussion about ice jams and subsequent ice flows on the river this winter. Starting after Christmas and moving into January, ice jams and flows took a toll on the Taylor and Gunnison Rivers. And while experts can explain how they formed, the cause remains a mystery.
“The only thing that seemed to be agreed upon was that one of the factors likely was the fact that temperatures were quite warm [early in the winter] so there was open water in late November and early December and then the weather turned dramatically colder. The icing experts say that open water in the channels was a key factor in allowing ice jams to form,” said Frank Kugel, general manager for the Upper Gunnison River Watershed Conservancy District.
Kugel said there were three different reports of ice dams: one between McCabe’s Lane and the Blue Mesa Reservoir after Christmas last year; a major event on the Taylor River on January 1 of this year that caused flooding and damage at Harmel’s and Almont; and another in mid-January.
The latter was “contained within the ice channel but it looked like a luge run there at Almont where the banks were covered with eight to ten feet of ice,” Kugel said.
“As a result of the second flow, a big chunk of ice got hung up at the Esty Ranch between Gunnison and Almont. It just sat there, a mile long block of ice as thick as 12 to 15 feet, reportedly, but that has been crumbling and deteriorating over the last couple of months and now does not appear to be much of a risk,” he added.
To assess the situation, Gunnison County brought in Dr. Steven F. Daly, a research hydraulic engineer with the Army Corps of Engineers. Daly is a river ice expert at the Corps’ Cold Regions Research and Engineering Laboratory in Hanover, N.H. He explained that the records show that the water flows into the Taylor River out of the Taylor Park Reservoir have been constant and that water released from the dam is slightly above freezing, or 32 degrees Fahrenheit.
When the ambient temperatures are as cold as they were in late December and January, that water reaches the freezing temperature within a few miles of the dam, and that’s when ice can form. The Taylor River, Daly explained, “is turbulent, very well mixed, and what’s happening is that the water actually becomes slightly super-cooled, or slightly below the freezing temperature.”
That turbulent, super-cooled water forms small, randomly oriented disk-shaped ice crystals known as frazil ice. Frazil ice can become deposited on the bottom of the river, where it’s known as anchor ice, and on features within the river. That can cause impediments to the river’s flow, raising the surface of the water.
The unusual events in the Gunnison and Taylor Rivers were a series of ice runs leading to ice jam formation in December and January. Typically, Daly said, ice runs occur when the ice cover becomes weak or there’s an increase in the channel flow. “If the ice cover is weakened it’s usually when the air warms up above 32 degrees.”
That wasn’t the case, however, on the Taylor and Gunnison Rivers. Daly visited Gunnison on February 2 and the temperature had been consistently cold. While there was some discussion about whether groundwater coming into the river could have been warmer and caused the ice to move, nothing was conclusive. The cause remains a mystery.
”The ice formation seemed fairly typical but why the ice ran and started moving and went downstream and jammed up we don’t know,” Daly said. He noted that his official report read, “It’s not clear what caused the ice runs in the Gunnison River this winter. It’s very unusual to have an ice run during sustained cold periods.”
