OMAHA, NEB. (AP) — The U.S. Army Corps of Engineers’ Omaha District has reached its goal of having the Missouri River mainstem levee system restored to its full height following massive flooding a year ago that devastated areas of Nebraska, Iowa, Kansas and Missouri.

While there is still much work to be done throughout the region, crews had closed 24 breaches along the main river system by March 1, spending more than $400 million to date on the work, Corps officials said Friday in a news conference in Omaha.

“It’s been an enormous task,” district commander Col. John Hudson said. “We moved 4.73 million cubic yards of sand. That’s equal to two Empire State Buildings.”

While the levees along the main system have been restored to their full elevation, they won’t be considered fully restored until grass can take root on them in warmer weather, Hudson said. The grass will help stymie erosion.

Flooding caused more than $3 billion in damage along the lower Missouri River last year as releases from dams upstream combined with heavy runoff from rain and melting snow to damage levees and inundate land along the river. Prolonged flooding also caused significant damage along the river in 2011.