"The Great Mississippi Flood of 1927 was the most destructive river flood in the history of the United States. [...] The aftermath of the flood was one factor in the Great Migration of African-Americans to northern cities. During an era driven by racism, blacks built levees at gunpoint, starved in refugee camps and many were left to fend for themselves during the flood, while whites were rescued." From Wikipedia.
Charlie Patton sang incredibly powerfully about that flood (listen to how he snaps the bass string fiercely with his thumb!), and Dylan paid tribute to the flood and to Patton on a recent album. "High Water Rising" is also a horrifying, Biblical metaphor for the age in which Noah, or Patton, or Dylan/we have lived.
[Photo of Patton: http://www.furious.com/perfect/charliepatton.html]