In the Great Mississippi Flood of 1927 the Mississippi River broke out of its levee system in 145 places and flooded 16,570,627 acres. 27,000 square miles were inundated up to a depth of 30 feet. The flood caused over $400 million in damages and killed 246 people in seven states.
The flood began when heavy rains pounded the central basin of the Mississippi in the summer of 1926. By September the Mississippi's tributaries in Kansas and Iowa were swollen to capacity. On New Year's day of 1927 the Cumberland River at Nashville topped levees at 56.2 feet.
By May of 1927 the Mississippi River below Memphis, Tennessee was a watery oval up to 60 miles wide.
The flood propelled Secretary of Commerce Herbert Hoover into the national spotlight and set the stage for his election to the Presidency.
As the flood approached New Orleans, Louisiana 30 tons of dynamite were set off on the levee at Caernarvon, Louisiana and sent 250,000 cubic feet of water per second pouring through. This prevented New Orleans from experiencing serious damage but destroyed much of the marsh below the city. 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 dynamiting, made it impossible for flood waters to seriously threaten the city.
By August 1927 the flood subsided. During the disaster 700,000 people were displaced, including 330,000 African-Americans who were moved to 154 relief camps. Many African-Americans were detained and forced to labor at gunpoint during flood relief efforts.The aftermath of the flood was one factor in the Great Migration of African-Americans to northern cities.