Ohio’s Rise Triggers Mississippi Flood Warnings Into Louisiana

When it comes to commerce, there are few things in the U.S. that can match the reach and power of the Mississippi River and its tributaries.

Everything from grain to coal to chemicals flow up and down the river, the nation’s shipping superhighway. Like any other artery, it can fall victim to the whims of weather, and this year is no exception.

The Ohio River, which feeds about 60 percent of the Mississippi’s flow south of Cairo, Illinois, is flooding because of melting snow and heavy rain across the Ohio Valley, said Jeff Graschel, service coordination hydrologist with the Lower Mississippi River Forecast Center in Slidell, Louisiana.

On a river, a flood moves through the water like a bowling ball through a snake. The rolling bulge can be seen coming days in advance, and yet sometimes even the best preparations aren’t enough to save the day.

Right now, the river is falling in Cincinnati, and the swell will continue down the Ohio before turning south at Cairo and setting out for the Gulf of Mexico.

The current forecast doesn’t call for a repeat of the overflow of 2011 that set records in many places, including Vicksburg, Mississippi, but major flooding may occur throughout the lower portion of the river.

“We’re not expecting anywhere near those levels,” Graschel said.

Midwest Melt

The snow that had fallen across the Midwest is mostly gone now, according to the National Operational Hydrologic Remote Sensing Center in Chanhassen, Minnesota. As a result, there won’t be a large melt-off later to combine with heavy spring rains.

As of Monday, only 9.5 percent of the contiguous U.S. was covered by snow, and almost all of that was in the Northeast, where Boston achieved a snowfall record this weekend with 108.6 inches (2.8 meters) for the season.

“We have got a lot of questions about the Northeast, but that doesn’t flow into the Mississippi,” Graschel said.

While the Ohio is often the dominant contributor to water in the lower Mississippi, it typically takes high levels from both the Ohio and from the upper Mississippi, which combines with the Missouri River north of St. Louis, to spark a memorable flood further south.

The Mississippi and Missouri form the fourth-largest river in the world, and with their tributaries create a watershed that covers about 40 percent of the contiguous U.S., according to the National Park Service.

Wild Side

All the work the U.S. Army Corps of Engineers has put into controlling the Big Muddy makes it seem sometimes about as natural as the plumbing in the house. However, the river has a wild side that refuses to be tamed, and that became very apparent in 2011.

That year, the Corps, seeking to prevent flooding in New Orleans, had to open spillways along its banks, including the Morganza floodway that allows water to flow into central Louisiana and be drawn into the Atchafalaya River, which also empties into the Gulf. It was the first time since 1973 that the Morganza had been opened.

A flood along the Mississippi can have an enormous impact on the movement of goods across the U.S. Barges on the Mississippi handle about 60 percent of the nation’s grain exports entering the Gulf of Mexico through New Orleans, as well as 22 percent of its petroleum and 20 percent of its coal.

Crossing Places

Beyond that, as the water spills from its banks it can cut highways and rail lines. Almost everything on the ground that moves from one end of the U.S. to the other has to go over the Mississippi at some point.

Flood warnings and advisories are posted along the banks of both rivers all the way down to Louisiana, the National Weather Service said.

Moderate flooding has begun in Cairo, the weather service said. The river gauge was at 47.52 feet on Monday and is expected to reach 48.5 feet Wednesday, 8 feet above flood stage.

At the southern end of the river, the Corps of Engineers will probably enter Phase I flood control by Tuesday. The Corps will then begin inspecting levees, and any excavations or pile-driving within 1,500 feet of a levee will also require a permit to continue, said Ricky Boyett, spokesman for the Corps New Orleans District.

The maximum crest is forecast for 14 feet by the March 31, which is a foot below where the Corps would enter its second phase.

Graschel said while the current flooding is more in line with the river’s typical ebb and flow, it should raise everyone’s level of awareness.

“We have to keep a close eye on things,” Graschel said. “If we do get a significant amount of rain, things could change.”

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