Baton Rouge and New Orleans exist because of the Mississippi River, and huge swaths of the region's and nation's economy have always depended upon it. But the big river didn't always flow where it does now.
And, if it wasn't for a 60-year-old collection of dams, gates, floodways and channels called the Old River Control Structure, the Mississippi probably would have moved away from those cities already.
Located in the notch of Louisiana's boot, where the Mississippi, Red and Atchafalaya Rivers meet, the structure probably prevented the Mississippi from switching course and sending the majority of its flow down the Atchafalaya River in the late 1970s or early '80s, the Corps of Engineers officials who run it say.
The Old River Control Structure's battle to keep the Mississippi, Atchafalaya and Red frozen in their places, circa 1950, has endlessly drawn the interest of writers and researchers who see in it as a potent symbol of humanity's struggle to bend nature to its will.
"Nature, in this place, had become an enemy of the state," the writer John McPhee concluded in his 1989 book "The Control of Nature," which examined the Old River complex and other attempts by people to tame nature.
Some researchers who study the Mississippi say the Corps can't stop nature, and someday the Mississippi will move. But Corps officials are confident they and Old River remain up to the task and that a change of the Mississippi's course is extremely unlikely any time soon.
Still, after decades of fighting nature, Old River is under more pressure than it has ever been, Corps officials say.
"We've been having floods at the highest frequency we've ever had before, so these structures are under a considerable load, you know, more frequently than ever," said David Ramirez, chief of the Corps’ river engineering branch in the New Orleans District. "And, they're not young."
Facing those realities, the Corps is planning a major inspection that will involve temporarily cutting off a crucial structure, known as the Low Sill Structure, from the Mississippi River. Engineers will make sure the structure is still strong enough to keep the Mississippi where Louisiana needs it to be.
"They were put in operation in the '60s," he added, "so just looking towards the future, if we're going to continue to have floods at this frequency and this magnitude, it was just decided that it's probably prudent to just, let's dewater it and get in there and just to make sure we can feel confident we have a structure in place that can do what it's supposed do."
The strain of flooding
The last time the Corps did work like this, it was after the Low Sill Structure came close to failing.
The flood of 1973 caused one of Low Sill's guide walls to collapse and scoured beneath a wide area of its foundation, down into its steel support piers. The Morganza Spillway had to be opened downriver to relieve pressure. In 1987, the Corps blocked off the Mississippi to make major repairs to the Low Sill.
Even after the repairs, Low Sill couldn't handle as much pressure from floodwaters as it previously could. So, before those repairs began, the Corps built the Auxiliary Structure to compensate.
The incident shows the strain major floods can place on Old River. Since then, the complex appears to have handled major floods in 2011 and 2019 with no major damage.
But with climate change causing more severe weather events, the Corps is planning for more big floods in the future.
To closely study the Low Sill, the Corps plans to construct a large coffer dam, likely earthen, to block off river water from the 566-foot long structure, which normally stays covered with water, allowing the Mississippi to flow over it to the Red and Atchafalaya.
Corps officials are still working out the details of the dam and the planned inspection, as well as any potential repairs and the handling of floodwater during the work, Ramirez said.
Underwater inspections are already done regularly, but Corps officials believe removing all the water around the Low Sill will provide a much better look and offer the ability to make necessary repairs.
Ramirez pointed out the work will be done during the Mississippi's traditional low-water period, starting in August, and will probably last no more than 90 days.
"We don't want to have it dewatered going into the winter because that's when the rain starts and the water, the river begins to rise," he said.
Holding back nature
For millennia, the river had flopped around across south Louisiana like a garden hose at full blast. It switched course every thousand years or so to find steeper, more direct routes to the Gulf of Mexico as the old routes became elevated and clogged with silt.
These cyclical natural forces have had some help from humans at Old River.
The removal of great logjams in the Red and Atchafalaya rivers helped unplug those waterways in the 1800s. Along with the earlier digging of a Mississippi short cut at Old River, the Atchafalaya, which eventually joined with the Red, was allowed to deepen, widen and begin to capture more and more of the flow of the Mississippi through the connection at Old River.
By the early 1950s, researchers realized that the Mississippi would begin flowing into the Atchafalaya, left to its own devices. That would mean that, eventually, the river would stop flowing past Baton Rouge and New Orleans in any significant way.
That fear is what spurred construction of the Old River complex.
The structures are designed to lock in the waters of that time: the combined flows from the Red and Mississippi above Old River are split 70/30 between the Mississippi and Atchafalaya below Old River.
The split maintains a full Mississippi able to support international river commerce and provide fresh water for more than 1.2 million people in the New Orleans region and numerous industrial facilities that power the state's economy.
How long will it last?
But Yi-Jun Xu, an LSU hydrology professor, believes a major flood or some other triggering event, will one day break the Mississippi loose — likely permanently.
Xu and other researchers produced provocative findings in late 2017 that the bed of the lower Mississippi, beginning a few miles below Old River, had risen 30 feet since 1992. Since then, he and others have shown the Atchafalaya below Old River is simultaneously deepening.
Combine that with slowing river speeds and the likelihood that climate change will dump more water into the river, and you have the seeds for the Mississippi's next great change, Xu argues.
"We believe the system will fail, sometime," he said.
Exactly when, he added, isn't known. But, if the river switched fully, flows would lessen greatly and the river could turn salty from the encroaching Gulf all the way to Baton Rouge.
Torbjörn Törnqvist, a Tulane University geology professor, noted the risks from hurricanes remain a greater immediate concern for the state. But he said that rising seas may increase the likelihood of a major river course switch, which is known in scientific circles as an "avulsion."
"There is some evidence from the geological record that avulsions become more frequent when rates of sea-level rise are higher," he said. "They also have a tendency to shift farther inland due to rising sea level."
The Corps' management plans for the river date back to the period after the Great Flood of 1927. Ramirez said Corps officials have heard concerns about the changing climate and the desires to take another look at the 70/30 split at Old River, in part, for coastal restoration.
The agency was authorized last year and is trying to line up funding for a comprehensive look at the lower Mississippi's management.
"And so, this is a big study to look at, to see: Is the system still adequate," Ramirez said. "Do we need another structure? Should we operate differently? What changes need to be made?"
Craig Colten, an emeritus LSU professor of geology who has spent his career studying Louisiana infrastructure and the battle with nature, drove over the Low Sill during the '73 flood as a curious LSU student. He remembers the harrowing feeling of the structure vibrating from the rushing waters.
He welcomes the Corps' new look at things but believes the agency is already behind attempts by other parts of the military to account of climate change. Infrastructure changes move slowly, Colten noted.
While the agency may have confidence from its past experiences at Old River, the future could bring new challenges.
"We still haven't had a flood that really, really significantly passes '27 or '73. I don't know that it's been fully tested, and I think with the amount of precipitation that we can have in a spring these days, it's gonna be tested," Colten said.