The Collaborative International Dictionary of English v.0.48:
floodhead \floodhead\ n. a wall of water rushing ahead of the flood; as, we were lucky to be safe when the floodheads hit.. [WordNet 1.5]WordNet (r) 3.0 (2006):
floodhead n 1: a wall of water rushing ahead of the flood; "we were lucky to be safe when the floodheads hit"