Scientists have long said the only way to restore Louisiana’s vanishing wetlands is to undo the elaborate levee system that controls the Mississippi River, not with the small projects that have been tried here and there, but with a massive diversion that would send the muddy river flooding wholesale into the state’s sediment-starved marshes.
Multimedia
Many scientists advocate diverting the Mississippi River below New Orleans, where towns like Pilottown, above, sit along the delta.
And most of them have long dismissed the idea as impractical, unaffordable and lethal to the region’s economy. Now, they are reconsidering. In fact, when a group of researchers convened last April to consider the fate of the Louisiana coast, their recommendation was unanimous: divert the river.
Far from rejecting the idea, state officials have embraced it, motivated not just by the lessons of Hurricane Katrina but also by growing fears that global climate change will bring rising seas, accelerating land loss and worse weather.
“A major diversion in the lower part of the river is something that needs to be done,” said James R. Hanchey, deputy secretary of the Louisiana Department of Natural Resources. He said the state was convening a planning meeting on the idea this fall. The diversion would be well downstream of New Orleans, in the bird-foot delta at the river’s mouth. Even so, there would be tremendous engineering challenges, particularly in finding a new way for freighters to make their way into the Mississippi’s shipping channel, said Mr. Hanchey, who took his job after retiring as director of engineering and technical services for the Mississippi Valley division of the Army Corps of Engineers. But he added, “I think it’s within the realm of possibility.”
Ellis J. Clairain Jr., interim director of the Louisiana Coastal Area science and technology program for the Army Corps, called the idea “a possible alternative.”
And Virginia R. Burkett, coordinator of global-change science for the United States Geological Survey and another participant at the April meeting, called it “the only practical solution.”
The diversion proposal was recommended by a panel of dozens of scientists and engineers from all over the world invited to Louisiana to view the state’s marshy coast and to envision its future, said Denise J. Reed, a coastal geologist at the University of New Orleans who organized the meeting.
“The thing is to stop wasting 120 million tons of sediment” the river carries into the Gulf of Mexico on an average year, Dr. Reed said. Because the bird-foot delta has grown so far into the gulf, she said, the river’s mouth is at the edge of the continental shelf. As a result, the sediment it carries ends up in deep water, where it is lost forever.
A diversion would send the river’s richly muddy water into marshes or shallow-water areas where, Dr. Reed said, “the natural processes of waves, coastal currents and even storms can rework that sediment and bring it up and bring it into the coast.”
“It’s a lot,” she said, enough to cover 60 square miles half an inch deep every year, an amount that would slow or even reverse land loss in the state’s marshes, which have shrunk by about a quarter, more than 1,500 square miles, since the 1930’s. Such a program would not turn things around immediately, “but every year new land would be built,” said Joseph T. Kelley, a professor of marine geology at the University of Maine, who took part in the April meeting.
As the bird-foot delta broke up, Dr. Reed said, it would provide needed sediment to the frail strings of barrier islands that line some of the Louisiana coast.
Another potential benefit, Mr. Hanchey said, would come from the substantial nutrient runoff from inland agriculture in chemicals that contribute to the so-called dead zone of oxygen-poor water near the river’s mouth. Applied to the marsh, the nutrients might encourage desirable plants, he said.
Designing such a diversion would be complex and time-consuming, and the experts who met in April did not even attempt it. Even this fall’s meeting is not to plan the project, but to plan how the project should be planned, Mr. Hanchey said. Though Louisiana is rich in experts on river, wetland and coastal science, he said, state officials hoped to recruit scientists and engineers from all over the world to tell them “what we would have to know before we could initiate work on something like this, and what we would have to do to gain that knowledge.”
In a way, the bird-foot delta is an artifact of engineering. Without the levees and other structures that keep the river in place, it probably would have taken another path.
Like many major rivers, the Mississippi has tributaries, which feed water into it, and distributaries, which carry water away from it as it nears its mouth. Its tributaries include the Missouri and Ohio Rivers; one way or another, every stream, storm drain and parking lot from the Rockies to the Appalachians drains into the Mississippi. But about 250 miles from the gulf, near Lettsworth, La., the river stops taking water in and starts feeding it out, into the gulf through the main stem of bird-foot delta but also in distributaries like the Atchafalaya River, which flows into Atchafalaya Bay to the west.
Until people interfered with its flow, the Mississippi’s path to the gulf silted up naturally over time; water flow slowed and the river bed lost its capacity to carry a big flood. When next the big flood came, the river would suddenly turn one of its distributaries into its new main stem.
This kind of switching has occurred roughly every 1,500 years, geologists say, and since about 1950 the river has been ready for a change — to the Atchafalaya. The Corps of Engineers prevents that from happening with an enormous installation of locks, dams and power stations near Lettsworth, north of Baton Rouge and about 100 miles northwest of New Orleans.
