Other options include elevating structures, a measure that is common in coastal areas, and flood-treating buildings, he said.
Flood plains, he said, should be revised regularly because “every new development that occurs somewhere in the flood plain or in the watershed in some degree or another affects what the 100-year flood plain looks like.
“It is not static,” he said.
The time to think about flood mitigation is before the flood ever occurs, he said. A city can develop a post-disaster redevelopment plan so it can move immediately after a flood or other serious event.
Along the Missouri, the Corps is sending out sandbagging machines to cities like St. Joseph, Mo., which had a 24-hour filling operation under way June 11 and 12, and has bought more than 3 million sandbags for distribution.
The Omaha District supervises almost 800 miles of levees, some of which are handled by private “sponsors” who maintain and monitor them for potential problems.
It provides backup for issues they can’t handle and is bringing in specialists from around the country during this period, Gross said.
Levees “can be breached for many reasons,” Ruch said. “At this point it is too early to tell what caused the breach” near Hamburg, Iowa.
The levee, operated by a local sponsor, is being backed up with the Ditch 6 levee that is being raised 4 ft. in a temporary risk reduction step.
“Our levees haven’t seen this type of duration,” Gross said. “We will have two months at high flows of 150,000 cfs. It’s the duration testing our levees, not the force.”
This year “will be a new data point in the history of the Missouri River Basin, both in terms of hydrology and flood plain impacts, so this event will certainly be studied in the future,” she said.