Thousands of people living along the Mississippi are evacuating their homes for higher ground, as the river approaches levels not seen in decades. Many more people are waiting for word on whether they should leave.
River levels are already higher than the great floods of 1927 and 1937. In eight states, communities that live by the river now live in it.
CBS News correspondent Mark Strassmann says communities like Finley, Tenn., will be grappling with rising waters for most of this month.
It has already begun in Memphis, where there has been some flooding downtown - and the Mississippi doesn't even crest there until Wednesday.
Memphis a "high-impact area"
In Tennessee, local authorities were uncertain whether they had legal authority to order evacuations, and hoped the fliers would persuade people to leave. Bob Nations, director of emergency management for Shelby County, which includes Memphis, said there was still time to get out. The river is not expected to crest until Wednesday.
"This does not mean that water is at your doorstep," Nations said of the door-to-door effort. "This means you are in a high-impact area."
About 950 households in Memphis and about 135 other homes in Shelby County were getting the notices, Shelby County Division Fire Chief Joseph Rike said. Shelters were opened, and the fliers include a phone number to arrange transportation for people who need it.
Graceland, Elvis Presley's home and one of the city's best-known landmarks, is about a 20-minute drive from the river and in no danger of flooding, spokesman Kevin Kern said. "We're on a hill, high and dry and open for business, and will stay open," Kern said.
Water pooled at the lowest end of Beale Street, the thoroughfare synonymous with Mississippi blues, but it was about a half-mile from the street's world-famous nightspots.
The main Memphis airport was not threatened, nor was FedEx, which has a sorting hub at the airport that handles up to 2 million packages per day.
Bea, the civil engineer, said he is concerned because some levees across the U.S. have been built with inferior dirt, or even sand, and have been poorly designed.
"The standards we use to build these things are on the horribly low side if you judge them by world criteria and conditions," he said. "The breaches, as we learned in New Orleans, are the killers."
How long the high water lingers, and how much damage it does to the earthen walls of the levees as it goes down, are crucial factors.
"The whole summer will have to be watched," said J. David Rogers, a civil engineer at the Missouri University of Science and Technology.
Above: U.S. Army Corps of Engineers crews build a levee in an agricultural field to hold water to counter sand boils along the levee system in Fulton County near Hickman, Ky., Friday, May 6, 2011. Flood water from the upper portion of the Mississippi River and the Ohio River is moving south on the Mississippi. (AP Photo/The Paducah Sun, Stephen Lance Dennee)
Since the Great Mississippi Flood of 1927, a disaster that killed hundreds, Congress has made protecting the cities on the lower Mississippi a priority. The Army Corps of Engineers has spent $13 billion to fortify cities with floodwalls and carve out overflow basins and ponds a departure from the "levees-only" strategy that led to the 1927 calamity.
The Corps also straightened out sections of the river that used to meander and pool perilously. As a result, the Mississippi flows into the Gulf of Mexico faster, and water presses against the levees for shorter periods.
Baton Rogue: Jindal says spillway may be opened
In Louisiana, state officials warned residents that even if a key spillway northwest of Baton Rouge was opened, residents should expect floods comparable to those of 1973. Some of Louisiana's most valuable farmland is expected to be inundated with water.
Louisiana Gov. Bobby Jindal said the Morganza spillway could be opened as soon as Thursday, but a decision has not been made. If it is opened, it could stay open for weeks.
A separate spillway northwest of New Orleans was to be opened Monday, helping ease the pressure on levees there.
The state's Department of Children and Family Services increased shelter space near the areas expected to be flooded and is preparing for extended stays.
"You could see the spillway opened up for a few weeks, so it is going to be important that these shelters are going to be available to these folks beyond just the few days that is normally the case with a hurricane evacuation," Jindal said.