Public Safety

Why the dam in Cedar Rapids doesn't affect flooding

All gates open at the 5-in-1 dam when Cedar River hits just 10 feet

The city of Cedar Rapids is creating a public relations video to share how the 5-in-1 dam works. Photographed in Cedar Rapids on Thursday, April 3, 2014. (Liz Martin/The Gazette)
The city of Cedar Rapids is creating a public relations video to share how the 5-in-1 dam works. Photographed in Cedar Rapids on Thursday, April 3, 2014. (Liz Martin/The Gazette)
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This story originally published in The Gazette on June, 23, 2014. It explains when the City of Cedar Rapids opens up the gates on the city’s 5-in-1 dam on the Cedar River.

CEDAR RAPIDS — One tall tale that lingers here is that a city official more adept in the operation of the dam at the base of the 5-in-1 bridge could have lessened the impact of the city’s flood disaster in June 2008.

In truth, the dam has little or nothing to do with flooding.

5-in-1 dam video

At about 6:30 p.m. Saturday, fact replaced fiction when a small crew of Water Division employees began the slow, methodical job of raising five, 60-foot-wide gates at the dam to let more of the rising Cedar River make its way through Cedar Rapids.

The task requires patience — each of the five steel gates is hoisted, one at a time, by electric motor, an exercise that in total takes about seven-and-half hours. But it requires little finesse.

As Tariq Baloch, the city’s water plant manager, explained above the dam Saturday night, engineering specifications built into the design of the 600-plus-foot-wide dam dictate that city crews begin the lumbering process of raising the five gates on the ends of the dam when the pool of water below it gets to 10 feet and the projection is that it will rise to some height above 12 feet.

The dam’s central role is to keep a pool of water above the dam at sufficient depth so that the river can support boating and other recreational activities behind it in the Ellis Park area and farther upstream.

In the middle of the dam also are four underwater gates, which automatically adjust, lowering or raising to maintain the pool of water above the dam, which is about 15 feet deep right above the dam.

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Those four center gates ­— not visible to an onlooker — completely lower, as they have now, when the pool of water below the dam has climbed to 10 feet and it’s time to raise the dam’s five end gates.

Once the dam’s five end gates are opened, the pool of water above and below the dam is at the same height, and so the dam’s gates no longer play any role in holding back or increasing the flow of water over it.

(A 10th gate on the east side of the river, which provided water to the city’s now disabled hydroelectric plant at the dam, remains closed).

Baloch said city crews raised the five outside gates on the dam at the same river height and in the same fashion back in 2008 as they did Saturday evening into early Sunday morning.

“This dam structure would not have prevented any of the problems back in 2008,” Baloch said. “If you were to look back at the photos, all the lift gates were out of the water, and there were no restrictions of water through the dam whatsoever. And the river continued to rise.

“We did this at 10 feet tonight. So think back to 2008. An additional 20 feet of water came down the river.”

Levels of severity

Flooding in Cedar Rapids has four categories of severity: action plan, minor flooding, moderate flooding and major flooding.

The action plan is when the river below the dam is between 10 feet and 12 feet, which requires the raising of the outside gates on the dam. Minor flooding is between 12 feet and 14 feet, moderate is between 14 feet and 16, and major is above 16 feet.

Before the June 2008 flood, when the river crested at 31.12 feet on June 13, the historic crests had been at 20 feet on March 18, 1929, and June 1, 1851.

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Last year, the river reached its 10th highest Cedar Rapids crest at 18.23 feet on June 2, which had city crews and volunteers scrambling to fortify areas in New Bohemia and other low-lying areas, but there was little damage.

By early afternoon Sunday, more rain in the Cedar River watershed north of Cedar Rapids bumped the National Weather Service prediction to 16.5 feet, just into the major-flood category.

Baloch said most years the Cedar River at Cedar Rapids rises to the action stage and above, necessitating the raising of the dam’s outside gates. The one recent exception was in 2012, he said.

To raise the dam’s gates, city workers enter a caged catwalk that runs directly above the length of the dam between the E and F avenue segments of the 5-in-1 bridge. On the catwalk, the workers monitor motors and the cables as the gates slowly disengage from the dam and rise. The workers also are looking for large trees and other debris that might hang up on the gates or prevent the gates from being lowered once the river level below the dam falls to 12 feet and it’s time to lower the gates.

“It’s a powerful natural force. It has its own will,” said Baloch, staring down through the see-through catwalk Saturday night as if for a first time as the river water hurdled over the dam.

Taking time to show close up how the dam operates might help answer some of the public’s questions from 2008, he said.

Outside a small utility building at the dam on the river’s west bank, a dozen or more fishing regulars had lines in the river Saturday night not sure if the newly opening gates would improve their catch or not.

Inside the building, Bill Connolly, a Water Division electronics technician, was sitting in spare quarters in a nicely padded office chair, monitoring gauges that slowly were showing how the level of the river above the dam and level below it were working to equalize as the gates of the dam were raised.

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Connolly said the gate-raising would be complete by 2 or 3 a.m. Sunday at a time when only a few fishing poles likely would still be at it outside as he headed home.

One high-water year, he said he walked out of the building early one morning to be greeted by a lone fisherman who had lugged in a carp nearly as tall as Connolly.

“It was up to here,” Connolly said.

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We value your trust and work hard to provide fair, accurate coverage. If you have found an error or omission in our reporting, tell us here.

Or if you have a story idea we should look into? Tell us here.