The ice jam responsible for the flooding around Bismarck-Mandan was an unpredictable surprise that is now starting to show signs of weakening, potentially relieving rising floodwaters, an expert said Wednesday.

Roger Kay, a hydraulic engineer with the U.S. Army Corps of Engineers who specializes in ice jams, toured the flooding caused by large chunks of ice lodged in the Missouri River on Wednesday before a team of demolitions experts tried to create a channel in the ice to relieve flooding in the surrounding area.

"The ice is showing signs of being more rotten," Kay said. "It's starting to turn a kind of a brownish color … it gives us a good indication that the ice is really starting to melt out and weaken in places. That's good news."

Kay flew from Omaha, Neb., to Bismarck on Monday after ice chunks in the Heart River began to flow into the Missouri River, creating the jam located south of Fox Island, extending for about a half-mile.

"That's the difficulty of ice jams - they're very unpredictable," said Kay, who has about 19 years of experience studying ice jams around the country. "You can't really predict when they're going to form and the severity of them."

State officials hired a demolitions team out of Idaho to blast holes in the ice with the hope that water would be able to flow through it again to relieve the flooding. But if the explosives don't work, Kay said officials have few other options to battle the ice jam besides waiting for warmer weather.

"On smaller rivers, there might be options to move equipment on the river, but the Missouri River, it's such a large river there really is no effective way to mechanically remove the ice," Kay said, adding that any decrease in flood levels should be considered a success.

Cecily Fong, a spokeswoman for the North Dakota Department of Emergency Services, said the ice jam south of Bismarck has been a "wake-up call" for emergency management officials.

"We've probably had ice jams on the river before, but because we're so few people, nobody noticed it," Fong said.

People downstream should be aware that floodwaters could rise slightly if and when the ice jam near Bismarck begins to break down.

"As far as dangers downstream, there could be a small rise in stage downstream," Kay said, adding that there is a very broad flood plain taking on water and that, "we're probably not going to see much of an increase should that jam release."

Paul Johnston, a spokesman for the corps in Omaha, said it is corps policy not to recommend using the explosives on ice jams "because it rarely does any good."

"If you do get it to move, you transfer the problem someplace else," Johnston said. "The decision to use any explosives would be up to the state of North Dakota."

Kay said that people should be "cautiously optimistic" because flood levels are decreasing, but that could change if another ice jam north of Bismarck breaks down too quickly.

Also, if temperatures dip into the single digits, the ice chunks causing the jam could freeze together, causing an even bigger headache for officials.

Kay described the ice jam near Bismarck as "moderate" in size, but is smaller than some of the jams that he has seen on the Yellowstone River and Platte River in Nebraska.

He said ice jams are common along tributaries that flow into larger rivers, such as the Heart River and Missouri River, adding that, "Any ice jam is significant because it can cause flooding behind it."

Marlin Petermann, the assistant general manager with the Papio-Missouri River Natural Resources District in Nebraska, said his department used explosives to mitigate ice jams in the 1990s.

In 1997, an ice jam formed overnight on the Platte River, forcing officials to take swift action by hiring demolition experts to use explosives to "chip away" at the jam.

"You don't know when they're going to occur and you don't know if they're going to occur," Petermann said.

Kay also co-authored a report in 1997 on the use of explosives on ice jams that suggests they can be a successful method of clearing ice, but not in every case.

Also, in order for ice blasting to be successful, the report says that there must be enough water flowing behind the jam to push the loosened ice, as well as space downstream for the ice to flow.

"For many years, blasting ice jams has been considered a measure of 'last resort,' one that might appease public demands for action, but at the same time would not be effective in decreasing flood damages," the report said.

Using explosives on ice to help mitigate flooding is believed to have started in Germany in the 18th century, according to the report.

For a complete listing of all Tribune flood coverage go to http://www.bismarcktribune.com/floods/

(Reach reporter Brian Duggan at 223-8482 or brian.duggan@bismarcktribune.com.)