Cedar River Ice Jams Depend Largely on Speed of Thaw, River Levels

By Hayley Bruce, Reporter

CEDAR RAPIDS, Iowa — Last March, Al Pierson's Flower Shop on Ellis Boulevard was a mere 12 inches from flood damage caused by an ice jam along Cedar River.

But heading into another thawing season, Pierson said he's feeling more at ease due to the city's modified flood protection plan, which now includes ice jams, and two construction projects intended to mitigate flooding in the area above Cedar Rapids's 5-in-1 dam.

Though ice jams are hard to predict and even more difficult to prevent, Cedar Rapids Public Works Manager Craig Hanson said Monday that ice jam preparations for this year already are well underway.

"Ice jams are totally unpredictable, (and) the duration of an ice jam is not forecast the same way a river level is," Hanson said.

"Just like a flood, there are multiple factors, but an ice jam is even more unpredictable from the point of view that it might be doing perfectly well for a five-minute period, and then all of a sudden it causes a blockage and you start to build up water."

How Ice Jams Happen

Jon Nania, U.S. Geological Survey (USGS) hydrologist, said ice jams typically occur during fast-thawing events that cause the ice to break up and float down the river until it reaches a point where it contracts, or there is a bend in the river, and the ice gets stuck. Because water continues to flow, an ice jam can cause water to pile up behind the ice — which in turn can cause flooding — until it can break loose.

Though it's too soon to say whether an ice jam will occur on the Cedar River this year, Hanson said many factors play a role in whether one will occur, including the speed of the thaw and whether it's raining during the thaw, which could contribute to higher river levels.

If the conditions are ripe, ice jams typically happen around the first week of March.

Nania said the USGS also is seeing thicker ice on rivers throughout the state, which could be a cause for concern.

"We're seeing it up to a couple feet thick in the river, which for rivers in Iowa is pretty thick," Nania said.

He said that thicker ice — caused by this winter's cold temperatures and lack of snow early on, which insulates the river from cold temperatures — could make for bigger ice chunks floating down the river.

"It would be harder for those larger chunks to break. If it was thinner, just a couple inches, it would be easier for bridge piers to break it into smaller pieces," Nania said. "But it could be harder for the river to break it up and possibly easier potential for ice jams."

Hanson said he's also concerned about thick ice creating a prolonged jam, though that also would depend heavily on what other weather conditions are in place during a thaw.

Previous Ice Jam Damage

Last March, an ice jam in the river above the 5-in-1 dam caused flooding in the northwest neighborhood below Ellis Park, prompting city crews to respond with pumps, sandbags and flood barriers to contain the water. Several roads were temporarily closed, and street crews were deployed to push ice chunks off Ellis Boulevard NW.

Water was in basements of some homes in the area, and the city's response to flooding was called into question, with the Northwest Neighbors Neighborhood Association and area businesses calling for a quicker response.

Pierson, whose Flower Shop is located at 1800 Ellis Blvd. NW, said water was within 12 inches of coming through his back workroom building, where the store's boiler and coolers are, before the city brought in pumps to control the water. He said several homeowners in the area, and his employees, were trapped due to flooding conditions that day.

Pierson's business wasn't damaged as a result of the flooding, and he said he's happy with the city's response after last year's ice jam.

"It's been a problem for 40 years, it never really was a big problem, but after the flood of '08 any time I see water coming in the street, I get a little scared, to put it mildly," Pierson said.

"After the problem last year, they were good and they got on it, and they have the plan and two construction projects which will start soon and hopefully will fix it for good and we have their attention and their action, so I think it will all be fine. I'm pleased with it."

Updated Flood Protection Measures

Hanson said flood preparations — which now include preparations for ice jams — started in December and that they are on schedule.

He said city staff has reviewed the preparations and will take action as the ice gets closer to breaking up on the river. Those preparations include pumps being moved for faster deployment in the City Service Center, supplies positioned for flood mitigation at structures on Eighth Street NW and pumps placed in northwest Cedar Rapids.

Hanson also said the city has 10,000 sand bags prepared.

Construction is set to begin on flood control valves at the intersection of Q and Ellis Boulevard NW next Monday, and Hanson said the city is working to modify the berm at the intersection of Eighth Street NW and Ellis Lane. But should something happen before it is complete, the city will build an earthen berm, if necessary.

Both projects are expected to help with flooding problems in that area.
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