The Air Force is raising its cost estimate to $420 million to repair and rebuild at Nebraska's Offutt Air Force Base following severe flooding that forced officials to scramble to save munitions and move aircraft to higher ground.

More than 130 structures were damaged by the Missouri River flooding at the base that houses the U.S. military's Strategic Command. Roughly 60 of those structures were damaged beyond repair and will need to be demolished, said John Henderson, assistant secretary of the Air Force for installations, environment and energy.

"It wasn't just the water, it was what was in the water," Henderson told the Omaha World-Herald. The floodwaters ran as deep as 9 feet (2.7 meters) in some places and left behind a toxic sludge at the base.

The latest estimate is $70 million more than the initial estimate issued last month as part of the Air Force's $4.9 billion federal funding request for disaster relief. The call for emergency funding would also cover damage from Hurricane Michael nearly leveling Tyndall Air Force Base in Florida last fall.

Henderson said $300 million would be designated to design and build new structures at the Offutt Air Force Base, while $120 million will go toward cleanup and the repair of structures that can be saved.

Most of the new facilities will be built on higher ground, if possible, Henderson said.

The two levees protecting Offutt that were overwhelmed by floodwaters this spring are slated to be raised through a $30 million project by the Papio-Missouri River Natural Resources District.

Henderson said it's important for the two-year project to move forward. Construction was expected to begin this spring, but it's been pushed back because of flood damage to the levees.

John Winkler, the district's general manager, said they're working with the Army Corps of Engineers to assess the damage. Winkler said crews will need dry weather and lowered river water levels to get started.

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Information from: Omaha World-Herald, http://www.omaha.com