A flood is a natural disaster wherein an overabundance of water encroaches upon a given area of land where it is normally dry. While entirely natural in many areas, its impact on humans can range from mild to devastating, depending on severity and preparedness.
Floods have often affected both global and national history. According to Flood geologists, the Great Flood of Noah's time is responsible for much of the geology of the Earth's surface. The Johnstown flood of 1889 (also referred to locally as the "Great Flood" in reference to the biblical flood) did much to highlight dam safety (or lack thereof) in the United States. Flooding along the Mississippi River in 1993 caused millions of dollars in infrastructure damage and agricultural loss.