National Flood Insurance Program’s Definition of a Flood
A) A general and temporary condition of partial or complete inundation of two or more acres of normally dry land area or two or more properties from:

1) Overflow of inland (creeks, rivers, lakes) or tidal waters

2) Unusual and rapid accumulation or runoff of surface waters from any source

3) Mudflows which are proximately caused by flood, as defined above, and are akin to a river of liquid and flowing mud on the surface of normally dry land areas, as when earth is carried by a current or water deposited along the path of the current.

B) The collapse or sinking of land along the shore of a lake or other body of water as a result of (rapid) erosion, waves or currents of water exceeding anticipated cyclical levels which result in flooding described above.