Missouri's Black River levee fails. Where floodwaters could hit next.

Record or near-record flooding is expected along stretches of the Ohio and Mississippi Rivers in the coming days as the central and south-central US struggles to cope with the peak of the 2011 flood season.

Record winter snows and prolonged cold that kept the ground frozen and unable to absorb the spring melt have combined with a week of pummeling rains from intense spring storms to flood fields and riverside communities.

The spring storms, which have brought tornadoes as well as floods, have prompted the governors of Arkansas and Kentucky to declare states of emergency.

In Poplar Bluff, Mo., which has received some 15 inches of rain over the past four days, levees protecting the town from floods on the Black River have been breached or overtopped in several places, forcing the evacuation of some 1,000 people. According to the Associated Press, the privately maintained levees that protect homes and farms near Poplar Bluff failed an Army Corps of Engineers inspection in 2008.

In the meantime, federal hydrologists are keeping a close eye on two flood crests – one working its way down the Mississippi and one on the Ohio River, which empties into the Mississippi at Cairo, Ill.

The Mississippi's largely snow-melt driven crest is expected to pass Cairo first, followed closely by the crest from the Ohio. The two are expected to move south in tandem along the lower Mississippi.

Over the next two days, this one-two punch is expected to bring record or near-record flood levels to a stretch of river from Smithland, Ky., on the Ohio to New Madrid, Mo., on the Mississippi, according to Noreen Schwein, deputy for hydrological services at the National Weather Service's Central Region Headquarters in Kansas City, Mo.

Officials with the US Army Corps of Engineers were sufficiently concerned about this pending aquatic onslaught that they were considering blasting a hole in a levee along the Mississippi just south of its junction with the Ohio. But they reportedly put off a decision after Missouri's attorney general went to court to block the move, arguing that some 130,000 acres of farmland would become inundated.

Hydrological 'perfect storm'

The challenge presented by a pair of closely-spaced, slow-moving crests is that they tend to back water up behind them, prolonging the time that levees are under stress and that communities upstream continue to face flood conditions, says the National Weather Service's Schwein.

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