The Collaborative International Dictionary of English v.0.48:

Overfall \O"ver*fall`\, n.
   1. A cataract; a waterfall. [Obs.]
      [1913 Webster]

   2. (Naut.) A turbulent surface of water, caused by strong
      currents setting over submerged ridges; also, a dangerous
      submerged ridge or shoal.
      [1913 Webster]