FLOOD PROTECTION

Major flooding three times more likely in Cedar Rapids this spring, National Weather Service reports

The severity of spring flooding depends on how much more snow we get and how fast it melts

Water from Lake Macbride flows over the spillway into the Iowa River at a First Day Hike at Lake Macbride in Solon on Tuesday, Jan. 1, 2019. Parks nationwide hosted guided hikes in an effort to encourage people to get outside and start the new year in nature. (Rebecca F. Miller/The Gazette)
Water from Lake Macbride flows over the spillway into the Iowa River at a First Day Hike at Lake Macbride in Solon on Tuesday, Jan. 1, 2019. Parks nationwide hosted guided hikes in an effort to encourage people to get outside and start the new year in nature. (Rebecca F. Miller/The Gazette)

CEDAR RAPIDS — Brace yourself, Cedar Rapids: The Cedar River in the city is three times more likely than usual to cause major flooding this spring, according to projections released Thursday by the National Weather Service.

The Cedar River has a 24 percent likelihood of reaching its major flood stage of 16 feet this spring, compared with the 7 percent historical average, the weather service’s Quad Cities bureau reported.

Other sites along the Cedar River show elevated moderate and major flooding risks, but Cedar Rapids and Conesville have the largest jumps in likely flooding, the research found.

Cedar Rapids City Manager Jeff Pomeranz said the city has put projects in place to reduce the effects of flooding.

They include the Sinclair levee project — a half-mile levee and flood wall, pump station and 4.4-acre water retention basin completed in 2017 — and storm sewer upgrades.

“This is something we are watching very carefully and are very concerned about,” Pomeranz said of possible flooding. But “we have a plan in place and the resources to protect the city.”

The weather service predicts the Iowa River also will experience spring flooding, with Marengo having a 22 percent likelihood of reaching its major flood stage of 19 feet, compared with the 6 percent historical average. But Iowa City’s odds of seeing major flooding are normal, the report shows.

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The reason Cedar Rapids has greater chances of reaching major flood stage than other forecast points along the river is because those stages are set based on impacts, service meteorologist Jessica Brooks said.

“Where major flood stage at Cedar Rapids occurs with streamflows around 50,000 cfs (cubic feet per second), at Cedar Bluff, similar flows (50,000 cfs) are right around moderate flood stage,” Brooks said. “So it doesn’t take as much to get to ‘major flood stage’ and thus a higher probability.”

Iowa City has a lower risk of major flooding because flow can be controlled by the Coralville Reservoir, she said.

The Weather Service computes historical risks using hydrological data from 1949 to 2012 and climate data from 1981 to 2010, Brooks said.

Thursday’s flood forecast was the first of the spring season, covering March through mid-May. The service plans to issue an updated flood forecast March 7.

The severity of the flooding depends a lot on the melting of the massive snowpack Eastern Iowa has accumulated.

Cedar Rapids had 42.2 inches of snow this season as of Tuesday, the most since 2007-08 and well over double the average of 20.9 inches. Trained spotters said they measured another roughly 4 inches in the city since then.

But the snow levels further north along the Cedar River may be a larger factor.

“The process of melting the snowpack will be essential to the severity of flooding that occurs this spring,” the weather service reported. “A faster melt combined with heavy springtime rains could cause high impact flooding, while a slow melt with little additional precipitation would cause flooding to be much less severe.”

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Other factors for spring flooding are snow moisture levels, soil saturation, rain predictions, ice jams and river levels, Brooks told The Gazette last week.

l Comments: (319) 339-3157; erin.jordan@thegazette.com

B.A. Morelli of The Gazette contributed to this report.

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