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How catastrophic flooding could change the course of the Mississippi River

June 01, 2019; 3:47 PM

Floodwaters rushing toward the rising Mississippi River forced the U.S. Army Corps of Engineers to make the decision to open the rarely used Morganza Spillway on Thursday, June 6, to divert part of the river's flow into the Atchafalaya Basin.

About 24,000 acres are expected to flood as the water is funneled from the Mississippi River into the Atchafalaya River, according to USA TODAY. Residents and landowners in the path of the expected floods were alerted about the possibility last week.

The Old River Control Structure, known as America's Achilles' heel to some, is a floodgate system which regulates the flow of water leaving the Mississippi River into the Atchafalaya River in Vidalia, Louisiana.

The Old River Control Structure lies on a rural stretch of the Mississippi River in Louisiana, a few miles east of the tiny town of Simmesport.

The system is designed to prevent the Mississippi River from permanently altering course down the Atchafalaya River, bypassing Baton Rouge and New Orleans, but current flooding could put a strain on the system and in a worst-case scenario make it fail, causing the Mississippi River to change course down the Atchafalaya River.

"If the Mississippi River changes its course during a major flood, it would be a disaster for shipping and economic impacts in New Orleans and the lower end of the waterway," AccuWeather Senior Meteorologist Alex Sosnowski said.

Mississippi River Flooding Lawsuit

This Aug. 2, 2018, file photo shows the Old River Control Structure. The state of Mississippi is suing the federal government for at least $25 million, claiming a federal dam complex in Louisiana that keeps the Mississippi River from changing course is harming state land. (AP Photo/Gerald Herbert, File)

Industries and agricultural interests use the Mississippi River to transport goods upstream and downstream. Grain is hauled downstream, while raw materials are hauled upstream. It is more cost efficient to ship it by barge rather than rail or trucks because tug boats can pull a dozen or more barges up and down the river. However, if the flow is too great or water is too shallow, the boats can't haul as much.

The US Army Corps of Engineers currently has the rivers and structures under control, but some wonder how long that will last.

The Mississippi River has been above flood stage in Louisiana at some points for more than four months now, which is the most consecutive days in modern history.

During flooding in 1973, the Old River Control Structure almost failed when a hole developed in the structure, causing part of it to collapse. The Army Corps of Engineers dumped rock behind the dam, narrowly preventing it from failing. If the dam failed, the Mississippi River would have most likely changed course that day.

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Map of part of the Old River Control Structure and lock. (Image via the Army Corps of Engineers)

Improvements were made following 1973 flooding, and it also led to the opening of the Morganza Spillway to help relieve the pressure.

The Old River Control Structure was tested again during the flood of 2011, and thanks to the improvements made to the structure, was able to withstand the flooding.

"That part of the Mississippi River is in the Delta region, so if unchecked, you could have the main channel of the Mississippi shift to the Atchafalaya during and after a flood. That is why they built those structures," Sosnowski said.

To prevent possible catastrophic failure of the Old River Control Structure on the Mississippi, the Morganza spillway is getting opened for only the third time in its history.

"They are going to be releasing water into the Morganza spillway later this coming week, in stages. They delayed the opening a week to give property owners time to prepare," Sosnowski said.


Potential flooding of the Morganza Spillway opening. (Photo: Courtesy of the Army Corps of Engineers)

They have only opened the spillway two other times, in 1973 and 2011, so when they do, Sosnowski said, it's historic.

Gov. John Bel Edwards has requested a federal emergency declaration as the Mississippi River and other waterways continue to swell. However, Sosnowski doesn't think these floods will be too much to handle for the structures unless heavy rain from a tropical disturbance were to become involved over the next few weeks.

"I don't think the Morganza spillway will fail. I'm not sure about the Old River Control Structure, but I doubt it. They would just release more water through it if they had to," Sosnowski said.

Gov. Edwards said the state will also begin the process of sinking a barge in Bayou Chene Thursday to mitigate backwater flooding in Iberville and other parishes. The barge will act as a temporary floodgate at Bayou Chene, a tributary of the Atchafalaya River, to stop the flow there once the Morganza spillway is opened.

Dams: History, anatomy and common reasons for failure
More rain during early June could push river levels higher, expand flooding in central US
Levee failures along Mississippi, Missouri and Arkansas rivers prompt mandatory evacuation orders
Tropical disturbance in western Gulf to pose threat to parts of US

The Bonnet Carré Spillway, which diverts water from New Orleans to keep the city dry, was also opened for the second time this year, which is the first time that has occurred since it was built following the epic 1927 flood.

Should the worst-case scenario of rainfall from a tropical disturbance currently in the western Gulf of Mexico become involved, levels on the lower Mississippi could approach that of the Great Flood of 1927.

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