If the Old River Control Structure Fails: A Catastrophe With Global Impact

May 14, 2019, 5:01 AM EDT

Above: The Auxiliary Structure, the keystone of the $1 billion Old River Control Structure, which keeps the Mississippi River from changing channels. The main channel of the Mississippi River can be seen in the distance. Image credit: U.S. Army Corps of Engineers.

Even as technology becomes an ever-bigger part of our world, the Mississippi River remains the very lifeblood of the American economy. If the river were to carve a new path to the Gulf of Mexico down the Atchafalaya River during a massive flood, extremely damaging short- and long-term impacts costing hundreds of billions of dollars would result, along with a dangerous threat to global food supplies.

As detailed last week in Part I of this series, America’s Achilles’ Heel: the Mississippi River’s Old River Control Structure, the ORCS was built to act as a bulwark against the Mississippi River’s natural inclination to carve out a new channel to the Gulf of Mexico. But as explained in Part 2 of this series, Escalating Floods Putting Mississippi River's Old River Control Structure at Risk, the ORCS is under increasing threat of failure due to a build-up of sediment near the structure that is plugging the river's channel and creating higher floods.

America became the world's greatest economy because it had a wealth of natural resources. But those goods needed the world's greatest network of navigable rivers—the Mississippi River system—on which to be transported. Naturally, that network of rivers needed a port at the ocean, to regulate the flow of goods into and out of the country. Between Baton Rouge and New Orleans, the Lower Mississippi River has four of the fifteen largest ports in America. Those ports handle over 60% of all U.S. grain exports to the world, thanks to the barges moving downriver. Going upriver, those barges transport the petrochemicals, fertilizers, and raw materials essential for the functioning of U.S. industry and agriculture.

Mississippi River
Figure 1. Louisiana as seen by the MODIS instrument on March 21, 2019. Flooding along the Lower Mississippi and Atchafalaya rivers was creating large sediment plumes in the Gulf of Mexico. Image credit NASA.

If the Old River Control Structure (ORCS) were to fail, barge navigation might be interrupted for weeks and possibly months. Barge traffic on the new mainstem of the river--down the Atchafalaya’s channel—would be limited or impossible during the initial months of the channel change, due to turbulent and dangerously unstable conditions. At the split in the river’s channel at the ORCS, the river would dump a massive amount of sediment, potentially blocking navigation downriver on the old Mississippi channel towards Baton Rouge and New Orleans. Navigation might still be possible for a few months after the event with extensive dredging efforts, but the blockage might become so great mere dredging may not keep a clear channel for barge traffic, requiring that a new navigation lock be constructed—a multi-year project costing $100+ million. Closure of the Mississippi to shipping would cost the economy $295 million per day, said Gary LaGrange, executive director of the Port of New Orleans, during the great flood of 2011. Closure for multiple months would cause a cascade of impacts across a broad sector of the U.S. economy, multiplying costs.

There would be no way for trucks and trains to replace the barge shipping capacity lost during such an event, since barges are able to carry huge quantities of commodities that are uneconomical to ship other ways. For example, a typical 15-barge load towed on the Mississippi River would require 1000 trucks or two 100-car trains to transport and equivalent amount of goods, according to the Army Corps of Engineers. There are simply not enough trucks and trains in the country to make up for the barge capacity lost, and even if there were, the cost of doing so would be prohibitive.

Freight flows
Figure 2. Trucks carry most of the tonnage and value of freight in the United States, but railroads and barge traffic on waterways carry significant volumes over long distances. Rail moves a large volume of coal between the Powder River Basin in Wyoming and the Midwest. The highest freight volume moved on inland waterways occurs along the Lower Mississippi River. Image credit: U.S. Bureau of Transportation.

A potential global food crisis

Failure of the ORCS and the resulting loss of barge shipping that might result could well trigger a global food emergency. The U.S. is one of the world’s largest exporters of grain, and 60% of that grain is transported to market by barges travelling on the Lower Mississippi River. A multi-month interruption in the supplies of more than half of U.S. grain to the rest of the world can be expected to cause a spike in global food prices, and potentially create dangerous food shortages in vulnerable food-insecure nations.

As I wrote in my 2016 post, Food System Shock: Climate Change's Greatest Threat to Civilization, the greatest threat of climate change to civilization over the next 40 years is likely to be climate change-amplified extreme droughts and floods hitting multiple major global grain-producing "breadbaskets" simultaneously. An interruption in U.S. grain exports due to failure of the ORCS, if it occurs during the same year that another major grain-producing nation experiences a serious drought or flood, could cause a frightening global food emergency. The impact might be similar to what was outlined in a "Food System Shock" report issued in 2015 by insurance giant Lloyds of London, with rioting, terrorist attacks, civil war, mass starvation and severe losses to the global economy.

Food map
Figure 3. Proportion of the total calories coming from the main four commodity crops (corn, wheat, rice and soy) by country. The U.S., China, India, and Brazil are the world leaders. Major crop-damaging droughts or floods hitting two or more of these nations simultaneously would be a serious threat to the global food system. Image credit: UK-US Taskforce on Extreme Weather and Global Food System Resilience, 2015.

Flooding of Morgan City and destruction of pipelines, bridges, and rail lines

A 1980 report by a team of scientists at Louisiana State University, “If the Old River Control Structure Fails? The Physical and Economic Consequences”, laid out in alarming detail the consequences of the failure of the ORCS. The transferral of the bulk of the flow of North America’s mightiest river to a new channel down the Atchafalaya River would cause the inundation and potential destruction of multiple towns along the new course. The biggest city threatened would be Morgan City (population 12,000), which lies at the mouth of the Atchafalaya, near the shores of the Gulf of Mexico. The city’s current levee system is not designed to handle the flood that would result, potentially forcing its permanent abandonment. At least six other small towns along the Atchafalaya with populations of less than two thousand people might also see their existence threatened. The loss of life in such a flood should be low, though, since all of these cities would receive sufficient warning time to evacuate.

Important natural gas and oil pipelines cross the Atchafalaya River, and creation of the new river channel for the Mississippi would destroy a number of these pipelines, along with multiple bridges, roads, and rail lines. Natural gas supplies Louisiana with 75% of its electricity, and serious interruptions in power could be expected to the vast industrial corridor that lies along the stretch of the Mississippi River between Baton Rouge and New Orleans. At least ten oil refineries and three major oil import sites lie in this corridor, along with hundreds of billions of dollars worth of petrochemical plants, grain elevators, and fossil fuel and nuclear power plants. Major gas pipelines, like the Texas Gas Transmission, move natural gas across the Atchafalaya to far-flung customers in midwestern and northeast states, and these would experience months-long interruptions. Interruptions might also occur for two major oil pipelines, Colonial and Plantation, which cross the Atchafalaya, carrying refined oil from Gulf Coast refineries to the East Coast.

Morgan City flood
Figure 4. The Atchafalaya River climbs against the floodwall at Morgan City, Louisiana, during the 2011 flood. Image credit: USACE.

Loss of fresh water to 1.5 million people

In the long run, the Mississippi’s switch to a new channel down the Atchafalaya will leave so little flow going down the old channel past New Orleans that the final 200+ mile-long course of the current river will become a salt-water estuary of the Gulf of Mexico. The New Orleans, Metairie, Kenner, and Houma-Bayou Cane-Thibodaux metropolitan areas, which collectively include nearly 1.5 million people, would lose their main source of fresh water. Salt water from the Gulf might eventually penetrate 230 miles upriver to Baton Rouge, threatening their fresh water supply. Power plants and riverside industries would need up to two years to refit their systems for salt water, since salt water is corrosive. While beneath-ground aquifers do supply some of the fresh water needs of the region, additional fresh water sources would need to be tapped. One possible source might be the West Pearl River, located about 35 miles east of New Orleans.

A radical idea: let the Mississippi change channels in a controlled fashion

In 1983 engineer John D. Higby Jr. wrote a study called Possible Capture of the Mississippi by the Atchafalaya River. He stated that capture of the Mississippi River by the Atchafalaya was inevitable, and he questioned the Corps' assertion that the present status quo could be maintained into the “foreseeable future”. Higby recommended the creation of a congressional commission "made up of the world's foremost professionals in river engineering, geology, and water resources policy and planning" to make recommendations on the future of Mississippi River policy. His most eye-opening recommendation was to consider allowing the river to change its course slowly and under controlled conditions at Old River, and eventually abandon the Old River Control Structure, perhaps over a period of 50 to 100 years.

Other experts, such as Corps of Engineers geologist Charles R. Kolb and retired University of Illinois ecologist Richard E. Sparks, have echoed similar ideas. Said Sparks in his essay, Rethinking, Then Rebuilding New Orleans, "the most sensible strategy is to work with the forces of nature rather than trying to overpower them." He argued that by slowly allowing the Mississippi to change course, the Army Corps could engineer the desired channel for it to take down the Atchafalaya basin, and protect cities like Morgan City that might get wiped out if the river were allowed to establish its own new course in a future super flood that overwhelmed the ORCS. Similarly, the various pipelines, bridges, and other infrastructure crossing the Atchafalaya basin could be slowly moved or strengthened in a controlled fashion rather than being destroyed and then completely rebuilt after a flood catastrophe.

Sparks advocated building stronger flood defenses to protect the highest parts of New Orleans from Mississippi River floods and hurricane-generated storm surges, while retreating from the lowest parts. The flood-prone areas below sea level could be converted to parks and planted with flood-tolerant vegetation and allowed to flood temporarily during storms. The city would have to find a new source of fresh water—perhaps from the West Pearl River. This would be difficult, but not impossible. The “old” New Orleans would remain a national historic and cultural treasure, while a new port city could gradually be built on higher ground at the mouth of the Atchafalaya River, where sediment from the Mississippi is already forming new land through natural processes.

In an interview, Dr. Sanjeev Joshi, who wrote his 2017 Ph.D. thesis on the sedimentation problems by the Old River Control Structure, said he was not in favor of allowing a controlled shift of the Mississippi to a new channel down the Atchafalaya. Assuming that a solution to the excessive sediment problem could be found, Dr. Joshi stated that the ORCS and the levees surrounding it were so strong that there was perhaps just a 1% chance that the river would jump to a new channel in the next 100 years.

Commentary: plan for the eventual failure of the Old River Control Structure

Given the importance of the Old River Control Structure, the increasing flood threat it is facing due to increased sediment deposition, and the potential for increased Mississippi River flow rates due to climate change, it would be an excellent idea to create a congressional commission made up of the world's foremost professionals in river engineering, geology, and water resources policy and planning to make recommendations on the future of Mississippi River policy. Lousiana's ambitious 2017 Coastal Master Plan, which lays out plans to spend $50 billion over the next 50 years to protect the coast of Louisiana, makes no provision for a potential failure of the ORCS, and it should. Inevitably, the Mississippi River will change its channel, and we should make thoughtful plans on how to respond, whether the event happens next year or 100 years from now.

Related works

Part 1 of this series: America’s Achilles’ Heel: the Mississippi River’s Old River Control Structure
Part 2 of this series: Escalating Floods Putting Mississippi River's Old River Control Structure at Risk

Beyond Control: The Mississippi River's New Channel to the Gulf of Mexico, James Barnett Jr.’s detailed 2017 book.
John McPhee's 1987 essay, The Control of Nature.
Divine providence: the 2011 flood in the Mississippi River and Tributaries Project, by Army Corps historian Charles Camillo.


The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

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Dr. Jeff Masters

Dr. Jeff Masters co-founded Weather Underground in 1995, and flew with the NOAA Hurricane Hunters from 1986-1990.


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