Source : Webster's Revised Unabridged Dictionary (1913)

Flashboard \Flash"board`\, n.
   A board placed temporarily upon a milldam, to raise the water
   in the pond above its usual level; a flushboard. [U.S.]

Source : WordNet®

flashboard
     n : boarding place along the top of a dam to increase its height
         [syn: {flashboarding}]