GRAND FORKS, N.D. – As much as people in the Red River Valley want the sun and warmth of an honest spring, the colder than average temperatures of recent weeks have kept record March snowfalls from rushing into the Red River and its tributaries.
That’s the good news. The bad news is that the freezing temperatures are contributing to a frequent problematic feature of floods on the Red River and its tributaries: ice jams.
One ice jam last week on the Red Lake River at Crookston, Minn., caused a sudden spike in the river level, prompting city officials to recommend evacuation of at-risk parts of town until the jam broke up and the river level receded. A jam on the Red River has ice backed up behind a bridge at Thompson, N.D., south of Grand Forks.
Another Red River jam, estimated at 4 miles, continues to threaten bridges in Oslo, Minn., an island now behind its communal ring dike. Early this week, a Minnesota National Guard Chinook helicopter repeatedly lowered a 4,000-pound weight onto one stretch of ice at Oslo, hoping to break it up enough to get it flowing north with the river.
It was quite a show, with a dozen Minnesota National Guard soldiers watching from the ground and a second helicopter, a Blackhawk, flying point for the Chinook.
“It broke the ice a little, but not enough to make a difference,” said Scott Kosmatka, a City Council member and leader of Oslo’s flood fight.
Jam remains – along with fears
Next, the city and U.S. Army Corps of Engineers tried setting construction excavators on one of the threatened bridges to grab at the ice there. But the jam remains, as do fears that with increasing river flows it could damage or even take out one or both of the city’s highway and railroad bridges.
How people deal with river ice jams depends on many variables, including the ice thickness, river flow rates and what’s happening upstream and downstream.
Kate White, a hydraulic engineer with the Cold Regions Research and Engineering Laboratory in Hanover, N.H., arrived in Fargo this week as part of a team assembled by the U.S. Army Corps of Engineers to track the formation and movement of ice in the Red River flood.
“The key is whether the ice jam is amenable to being broken up ahead of time,” she said. “Or are you just moving the jam downstream, or breaking the ice up too early only to have it freeze again?”
Risks with explosives
Explosives “are not always the first choice,” she said, as they may raise safety and environmental concerns and risks to levees.
“But explosives can be effective if used in a right way,” she said, citing a successful effort to break up Missouri River ice jams near Bismarck last week. Because the ice cover was solid, on average 3 feet thick, charges could be set into the ice. The North Dakota National Guard provided 160 pounds of C-4 plastic explosive, which was packed into 80 holes drilled in the ice. Later, helicopters dropped road salt onto other parts of the river ice to weaken it.
A better but more expensive response would involve structural changes, White said, including channel modifications and the strategic placement of dams and ice booms, which could control where jams form.
At public meetings after the disastrous 1997 Red River flood, the International Joint Commission (IJC) heard many suggestions on how to deal with ice jams. In a 2000 report (PDF) prepared for the commission, researchers found that certain river features, such as the Red River’s hairpin curves and slight gradient, “are highly conducive to jamming.”
River ice can erode stream banks as well as make flood forecasting difficult, the report states. “Small bridges can be swept away,” and approaches may erode.
Manitoba springs for $1.2 million ice-breaker
After warnings earlier this month of potential major flooding on the Red River, Manitoba paid $1.2 million for an Amphibex ice-breaking machine, a sort of floating backhoe that claws through river ice with an articulated arm.
The machine joined one operated by two small municipalities and the city of Selkirk to work last week on a jam north of Winnipeg. The ice had backed up the Red River and caused flash flooding, forcing more than 30 families from homes in the municipality of St. Andrews.
According to a company Web site, the Amphibex was designed in Quebec and can be used to clean contaminated waterways, install pipelines and underwater cables and do dredging work. It is “highly effective” for breaking up and preventing ice jams and making it “unnecessary to use dynamite, which can harm the environment,” according to the company site.
But it’s expensive, and it can’t be used in all ice jam situations.
Mitigations include sand, salt, chemicals
The IJC, the Army Corps of Engineers and other agencies have identified other means of mitigating various types of ice jams, including the use of sand, salt, chemicals or drilling to weaken the ice or smoothing out some river curves, which was part of the Grand Forks-East Grand Forks permanent flood protection project after 1997.
Flood fighters may try to hurry ice breakup by dusting the ice surface with sand or chemicals to enhance the effect of solar radiation. But that has to be done long before the anticipated breakup, and any new snowfall could lessen the effect. The IJC report notes that one recent dusting on the Red River failed to hasten ice breakup because the sand was too light in color.
The challenge of ice on rivers at flood could be growing. The IJC report cautions that “very little work has been done on the more complex question of how climate change may influence the frequency and severity of ice jams.”
Chuck Haga, a reporter for the Grand Forks Herald, writes about western Minnesota and the Dakotas for MinnPost. He can be reached at chaga [at] minnpost [dot] com.
