Enlarge Nati Harnik/AP

The rising Missouri River swallows a home in Hamburg, Iowa, this week.

Nati Harnik/AP

The rising Missouri River swallows a home in Hamburg, Iowa, this week.

America's largest rivers have wreaked havoc on the Midwest this spring, inundating towns and farmland from South Dakota to Louisiana. Nature is responsible for most of it — huge snow packs in Colorado and Wyoming, and historic levels of rain. But some of the flooding isn't natural; it's controlled by the Army Corps of Engineers.

On the Corps call, hundreds of miles of farmland and parts of Louisiana were flooded to spare large cities farther down the river. The engineers also decided to keep water behind the dams of the Missouri River in the north to help out residents along the Mississippi. Those reservoirs are now dangerously close to capacity, and the Corps has just made another tough choice.

Saturday morning, for the first time in history, the Corps opened all the emergency outlets on six dams beyond their maximum recommended flow levels to keep the dams from collapsing.

It's hard enough to choose who gets wet and who stays dry. Harder still, some say, are bureaucratic rules that require the Corps to consider priorities other than flood control.

Who Gets Wet

Many homes and farms along the Missouri River are expected to be under at least some water. Farmer Don Diltz of Glenwood, Iowa, was one of the first to feel the effects earlier this week.

"Flooding is a part of life down here; you take that and accept it and move on," he says. "But this is unique. Most floods come and they leave; this flood's coming and it's going to stay for six months."

Jody Farhat, the chief of the Missouri River Basin Water Management Office in Omaha, is in charge of water management for the area.

"It's difficult to see the impacts of these historic releases on individuals and communities," Farhat says. "My staff and I are making those release decisions based on the information coming in every day."

These decisions are also made according to the Missouri Water Control Manual, referred to as the "master manual." It's a handbook written by the Corps with input from Congress, and it dictates the Corps' priorities. Some are easy to follow, like flood control, but others are more difficult to navigate, like keeping reservoirs full even when there's heavy snowpack, so tourists can take boats out and power companies can use water flow.

Too Many Priorities

That manual makes life tough for the Corps, which is bound by law to follow its recommendations, former Corps head Mike Parker says.

"It's a political document," he says. "Several years ago, Congress decided you have a lot of interests out there, and these interests got together and said, 'We're not getting represented.' So instead of having navigation and flood control as being the two primary things that the Corps was looking at, they had a list of eight things that they had to consider."

In addition to navigation and flood control, this list of priorities includes irrigation, water supply, hydropower, fish and wildlife, recreation and water quality. Parker says that some of these priorities run counter to each other.

"If the Corps only had to take care of navigation and flood control, I guarantee you those levels [in the Missouri River reservoirs] would have been much lower," he says.

The choices the Corps has made in recent months have impacted millions of lives along the Missouri and Mississippi rivers. Parker says that the decision to open the Morganza Spillway in Louisiana last month came at a cost.

"Gen. Mike Walsh had to stand in front of people and say, 'People, I'm opening these floodgates and by the way, I'm going to flood your homes. We're going to flood your businesses; we're sorry.'"

"If these were easy choices, you wouldn't be interviewing me today," Parker says.

The Army Corp of Engineers expects to hit an all-time high with the release of 160,000 cubic feet of water per second from the Oahe and Big Bend dams early Sunday morning.