The Great Mississippi Flood of 1927 was the most destructive river flood in the history of the United States, with inundated in depths of up to over the course of several months in early 1927. The period cost of the damage has been estimated to be between $246 million and $1 billion, which ranges from $4.2–$17.3 billion in 2023 dollars.
About 500 people died and over 630,000 people were directly affected; 94% of those affected lived in Arkansas, Mississippi, and Louisiana, especially in the Mississippi Delta region. 127 people died in Arkansas, making it one of the deadliest disasters ever recorded in the state. More than 200,000 African Americans were displaced from their homes along the Lower Mississippi River and had to live for lengthy periods in relief camps. As a result of this disruption, many joined the Great Migration from the South to the industrial cities of the North and the Midwest; the migrants preferred to move, rather than return to rural agricultural labor.
To prevent future floods, the federal government built the world's longest system of levees and floodways. Then-Secretary of Commerce Herbert Hoover's handling of the crisis gave him a positive nationwide reputation, helping pave the way to his election as U.S. President in 1928. Political turmoil from the disaster at the state level aided the election of Huey Long as governor in Louisiana.
Events
By the late nineteenth century, the United States was well aware of flooding potential along the Mississippi, which drained 40% of the nation's area. The Mississippi River Commission was established by the federal government in 1879, with the directive to deepen the river channel, improve navigation, prevent major flooding, and increase river-based commerce. This commission recommended raising extensive levees along its channels to contain the flow, dismissing the advice of experts such as James Eads, who had directed the Saint Louis Bridge project in the 1860s. These critics predicted that compressing a swollen river between walls would increase its destructive potential.
Flooding began due to heavy rainfall in summer 1926 across the river's central basin. By September, the Mississippi's tributaries in Kansas and Iowa were swollen to capacity. On Christmas Day of 1926, the Cumberland River at Nashville, Tennessee, exceeded , the second-highest recorded level (a destructive flood in 1793 had produced the record level – ).
Flooding peaked in the Lower Mississippi River near Mound Landing, Mississippi, and Arkansas City, Arkansas, and broke levees along the river in at least 145 places. The water flooded more than of land, and left more than 700,000 people homeless. Approximately 500 people died as a result of flooding. Monetary damages due to flooding reached approximately $1 billion, which was one-third of the federal budget in 1927. If the event were to have occurred in 2007, the damages would total around $930 billion to $1 trillion (measured in 2007 U.S. dollars).
The flood affected Missouri, Illinois, Kansas, Tennessee, Kentucky, Arkansas, Louisiana, Mississippi, Oklahoma, and Texas. Arkansas was hardest hit, with 14% of its territory covered by floodwaters extending from the Mississippi and Arkansas deltas. By May 1927, the Mississippi River below Memphis, Tennessee, reached a width of . Without trees, grasses, deep roots, and wetlands, the denuded soil of the watershed could not do its ancient work of absorbing floodwater after seasons of intense snow and rain.
Attempts at relief
In an unrelated flood at the same time, on Good Friday (15 April 1927), of rain fell in New Orleans in 18 hours. This far exceeded the City's rainwater pumping system, and up to of water flooded some parts of the city. This local rain related flood was not connected to the Mississippi River flooding.
A group of influential bankers in New Orleans met to discuss how to guarantee the safety of the city, as they had already learned of the massive scale of flooding upriver. On 29 April they arranged to set off about 30 tons of dynamite on the levee at Caernarvon, Louisiana, releasing of water. This was intended to prevent New Orleans from suffering serious damage, and it resulted in flooding much of the less densely populated St. Bernard Parish and all of Plaquemines Parish's east bank. As it turned out, the destruction of the Caernarvon levee was unnecessary; several major levee breaks well upstream of New Orleans, including one the day after the demolitions, released major amounts of flood waters, reducing the water that reached the city. The New Orleans businessmen did not compensate the losses of people in the downriver parishes.