Hydrologist: No flood danger for Lower Mississippi

Published 4:40 pm Thursday, June 26, 2008

While the Midwest continues its struggles with Mississippi River flooding and its aftermath, residents to the south along the Lower Mississippi have little to fear from the high water.

The Lower Mississippi, which begins at Cairo, Ill., is much deeper and wider that the river’s upper stretches through Illinois, Iowa and Missouri where flooding has caused at least 24 deaths and millions of dollars in damage.

“Our river is different from theirs. We have a much bigger flood plain. We have a better protected flood plain with our levee system and flood walls,” said Dave Beretta, a hydrologist with the U.S. Army Corps of Engineers.

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The Lower Mississippi, Beretta said, can carry more than 2 1/2 times the volume of water that the Upper Mississippi can handle.

Memphis, the largest city beside the Lower Mississippi, sits on high bluffs and faces little danger of flooding even when the river is at its highest and well above what the Corps considers flood stage.

At flood stage or “full bank,” the Lower Mississippi is still within its levee system, with flooding restricted to flood plains designed to take on high water.

“Once the river gets out of banks, when it gets to the levee that’s two and a half miles away,” Beretta said. “Where in that area up there, their levees a much closer.”

Thousands of acres of particularly rich farmland on both sides of the river in Tennessee, Arkansas and Mississippi are in the flood plains, and farmers who cultivate them take a gamble each year with flooding.

No major problems from the high water in the Upper Mississippi were expected in those areas.

“There’s been some agricultural flooding but it’s all within the levee system and that’s just the way the system is designed,” said Jim Pogue, a Corps spokesman. “We’ve got higher water right now than we routinely do this time of year so there’s more water inside the levee system.”

The Missouri River joins the Mississippi at St. Louis, aoward traditional summer lows that often register below zero.

With the river bottom constantly reshaped by the Mississippi’s powerful currents, gauges on the Lower Mississippi give no indication how deep the water is. Zero at Memphis is an arbitrary mark set in the 1800s at 183.91 feet above sea level.

The measurements let river watchers know when the Mississippi might overflow its banks or drop so low that shipping barges risk running aground. The river’s depth varies considerably from nine feet in barge channels maintained by the Corps of Engineers to more than 100 feet deep off the Memphis riverfront.