Definition of Extraordinary Flood
One of those unexplained occurrences whose coming is not foreshadowed by the usual course of nature, and whose magnitude and destructiveness could not have been anticipated or provided against by the exercise of ordinary foresight. Jensen v, Buffalo Drainage Dist. of Cloud County, 148 Kan. 712, 84 P.2d 961, 965. One of such unusual occurrence that it could not have been foreseen by men of ordinary experience and prudence.
That's the definition of Extraordinary Flood in Black's Law Dictionary 6th Edition. Courtesy of Cekhukum.com.