Updated

Residents of Cedar Rapids are watching anxiously as the quickly rising Cedar River threatens to inundate their city with devastating floodwaters for the second time in just over eight years.

After days of sandbagging and erecting an extensive system of flood barriers, residents and officials in Iowa's second largest city were simply waiting to see how high the Cedar River would rise and what impact the flood would have.

Entire neighborhoods and the downtown area were largely abandoned as residents in low-lying areas heeded the city's call to evacuate. Schools were cancelled and many businesses were closed.

The river was expected to crest Tuesday at 23 feet, the second largest flood in the city's history, behind only that of June 2008. The river level had risen past 20 feet by midday Monday, or 4 feet above major flood stage.

Here's the situation in Cedar Rapids and other communities affected by the flooding:

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IS CEDAR RAPIDS READY FOR THE FLOODING?

Yes, city officials said at a Monday news conference. Mayor Ron Corbett said nearly 10 miles of temporary levees have been constructed in just days, and 250,000 sandbags have been filled and placed to protect homes and businesses. More sandbags were being filled Monday to beef up barriers around critical city infrastructure. The Fire Department has staged boats for water rescues on both sides of the river. The American Red Cross has opened two shelters, and a local official said more emergency workers are flying in to help.

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WHY IS THE CITY RELYING ON TEMPORARY STRUCTURES?

The city has struggled since the 2008 flood to secure the funding that would be necessary to create a comprehensive flood protection system for low-lying areas on both sides of the river. Residents voted down a sales tax increase that would help pay for it years ago. Now the city is waiting on Congress to authorize and appropriate the federal share of a plan to build the system along with investments from the state and the city. City Manager Jeff Pomeranz said lobbying for the federal money is a top priority and the project will be critical to the city's future. Iowa's members of Congress are expected to push for the financing in the coming days.

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HAVE RESIDENTS IN THE POTENTIAL FLOOD ZONES BEEN EVACUATED?

Officials estimate that about 50 percent of the people in those zones have left for temporary shelter elsewhere, but the officials didn't have a head count of those remaining. The mayor and other officials implored people to stay away from the evacuation zone, lest they be caught by gushing water should part of the flood protection system fail. Corbett said the city wouldn't force residents or businesspeople out of the area but asked them to use common sense in making decisions that could affect their safety and the safety of others.

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WHAT ABOUT THE NATIONAL GUARD?

It's been activated to help, and Police Chief Wayne Jerman said Monday the troops will be patrolling the evacuation zone and helping out at traffic control checkpoints to keep out unwanted visitors. Jerman also said the Iowa State Patrol and other law enforcement agencies have sent officers to help.

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HAS FLOODING BEGUN IN CEDAR RAPIDS?

Flooding has closed some roads on the outskirts but none in the downtown area. Downtown and other city bridges have been closed, however, and access to Interstate 380 is limited in some spots.

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WHAT'S THE SITUATION UPSTREAM?

The river crested Saturday night in Waterloo and Cedar Falls, which are about 55 miles upstream from Cedar Rapids. The water levels in Cedar Falls and Waterloo were slightly lower than had been expected, but they still reached levels that were second only to those in 2008. Black Hawk County emergency manager Lori Glover said Monday that the water was dropping slowly and likely wouldn't be back to below flood stage until Thursday. She said any damage estimates would have to wait until then. In Charles City, residents put flood-damaged items out on their curbs for pickup Monday.