TODAY what the Corps of Engineers calls “Project Flood” protects the lower Mississippi River valley from a flood considerably greater, the Corps says, than that of 1927. In its present form this plan has finally ended in compromise the great and bitter rivalry of James Eads, Andrew Humphreys, and Charles Ellet begun so long ago. But the plan itself has created a major new problem, and it also has serious flaws.
Over the years Project Flood has undergone many changes, but its engineering backbone remains the original 1928 law, the Jadwin Plan, which set standards for levees far higher and thicker than those of 1927, but did not rely on levees alone. Instead, it embodied the chief principle articulated by Ellet, that the river cannot be contained within levees. So in addition the Corps has built reservoirs on several Mississippi tributaries, and also allows the Mississippi itself room to spread out through a series of various flood control features.
On the main river, the plan’s northernmost flood control feature is a “floodway,” essentially a parallel river 5 miles wide and 65 miles long, running from Birds Point, Missouri, south to New Madrid, Missouri. The river enters it through a “fuse-plug” levee, a levee lower than those surrounding it that is designed to blow out in a great flood. (If it holds, the Corps will dynamite it.) This floodway diverts a maximum flow of 550,000 cubic feet of water per second. It has been used only once, in 1937. At New Madrid the water returns to the Mississippi.
For the next 250 miles of river, to the mouth of the Arkansas, the Jadwin Plan originally called for only stronger levees to contain the water. At the mouth of the Arkansas, where in 1927 the river carried its greatest volume, Jadwin wanted to build a second, massive floodway that would have run for 155 miles and inundated 1.3 million acres, in effect duplicating the natural flooding that had occurred before the Corps closed the Cypress Creek outlet in 1921. Not surprisingly, this plan aroused intense opposition in Arkansas and Louisiana, intense enough to force a search for another solution.
Eads had one. He had always insisted that shortening the river by making “cutoffs,” cutting across the neck of horseshoe bends, would move water much faster and thus lower flood heights. For decades the Corps and most civilian engineers had rejected Eads’ argument, but after the 1927 flood William Elam, an engineer for the levee board in Greenville, took up Eads’ call. The Corps and the Mississippi River Commission resisted, but Hoover, then president, was convinced that the proposal deserved a test. When Jadwin retired in 1929, the secretary of war recommended ten different men as chief of engineers. Hoover refused to nominate any of them and finally hand-picked the man he wanted, General Lytle Brown. The hydraulics laboratory previously opposed by the Corps was built, and tests there and observations of a natural cutoff confirmed Eads’ predictions. In the 1930s and 1940s the Mississippi River Commission made cutoffs that shortened the river by more than 150 miles, largely by eliminating a series of sharp curves called “the Greenville bends.” The cutoffs worked dramatically, and lowered flood heights 15 feet, obviating the need for the floodway that Jadwin had proposed.
The next feature of Project Flood appears at a point called Old River, halfway between Natchez and Baton Rouge, where the Atchafalaya begins to flow from the Mississippi to the sea. Here, Project Flood is designed to handle its maximum flow of 3,030,000 cubic feet per second by dividing the water.
To direct this flow, the Corps built the Old River Control Structure and, 20 miles south, the Morganza floodway, immense masses of concrete and steel designed to divert approximately 600,000 cfs each into the Atchafalaya. In 1963 a massive dam sealed off the natural flow between the Mississippi and the Atchafalaya; since then the Old River structure has controlled the flow between the two rivers. The Morganza structure has been opened only once, in the 1973 flood.
In total, Project Flood sends 1,500,000 cfs—the water diverted from the Mississippi plus all the flow of the Red River—down the Atchafalaya River, and two floodways that parallel it, to the sea. The plan allows 1,500,000 cfs to continue down the Mississippi toward New Orleans. This exactly reverses the old policy called for by the levees-only theory; prior to the 1927 flood, the Corps of Engineers had planned to separate the Atchafalaya entirely from the Mississippi, and send all flood water past New Orleans.
The final flood control feature is a concrete spillway at Bonnet Carré, 30 miles above New Orleans, designed to subtract a final 250,000 cfs from the Mississippi when it is in flood; guide levees direct the outflow across 7 miles of land into Lake Pontchartrain. This spillway was first used in 1937, when it carried 318,000 cfs, the most it has ever handled; it was also opened in 1945, 1950, 1973, 1975, 1979, and 1983. According to plan, then, no more than 1,250,000 cfs will pass the city of New Orleans.
But Project Flood has several weak spots, and its solutions have created at least one new problem. First, the Corps claims its plans will handle a flood greater than that of 1927, 11 percent greater in the vicinity of the Mounds Landing crevasse. This claim is based on the Corps’ official 1927 reading of 2,544,000 cfs at the mouth of the Arkansas. In fact, James Kemper and several other civilian engineers independently measured the flow there at over 3,000,000 cfs. Even Army engineers, before being ordered by Jadwin to design an inexpensive plan, unofficially put the flow at over 3,000,000 cfs. This flow exceeds the design capacity of Project Flood by more than 100,000 cfs.
In addition, the levee system falls short of its design specifications. In 1996 there were 1,608 miles of main-stem Mississippi levees; 304 miles of those levees did not meet the design height. Most of these low levees fell only 1 to 2 feet below grade, but several miles of the levee system between Greenville and Vicksburg, on both the east and west banks, fell 6 feet short.
Another problem exists with the cutoffs. The river has not accepted them as final. In the fifty years since cutoffs shortened the river by 150 miles, the river has regained roughly one-third of that length and eroded some of the benefits.
But the greatest problem by far is the Atchafalaya, which offers a much shorter route to the sea, and a steeper slope, than the main channel of the Mississippi. The 1927 flood sent vast amounts of water down it, scouring it out, deepening it, building a channel capable of accommodating—and hungry for—far more water than it had ever carried. Project Flood puts even more water down it. Kemper warned that “the inevitable consequence” of this approach would be that the Atchafalaya “will soon become the main stream [of the Mississippi], and the river past New Orleans a deteriorating outlet.”
Kemper was not merely theorizing. The mouth of the Mississippi River has shifted many times. Twenty-five years after his warning, it became obvious that he was right, and in 1954 Congress passed emergency legislation to give the Corps money to prevent the Atchafalaya from claiming the entire Mississippi River. Keeping the Mississippi in its old channel has become by far the most serious engineering problem the Corps of Engineers faces. The Old River Control Structure was built to solve it, but the 1973 flood almost destroyed the structure by scouring out a hole 75 feet underwater that came close to causing its collapse. Many engineers believe that sooner or later, no matter what man does, the Mississippi will shift its channel to the Atchafalaya. And a finger of the sea will climb north past New Orleans, north to Baton Rouge.
So the story ends as it began, with man determined to assert his will over the river.