Flooding in the United States is the most common and costliest natural disaster in the United States. On average, about 140 deaths and $6 billion in property damages result from flooding events. The map to the left shows the number of Presidential disaster declarations related to flooding events by state; Green = 1 declaration, Yellow = 2, Orange = 3 and Red = 4 from 1965 - 2003. This shows that the majority of the country is to some degree vulnerable to flooding, making it a national safety issue.
The types of floods include:
Regional Floods - These floods can occur seasonally because of snow melts and spring rains or as a result of extended wet periods.
Ice-Jam Floods - This type of flood occurs on rivers that are totally or partially frozen. When stream gauge rises, a partially frozen river breaks up resulting in ice flows that can pile up on channel obstructions such as debris or shallow riffles. Water continues to build up behind the ice dam causing overflowing of upstream river banks. When the ice dam fails, a large wave of water rushes downstream causing dangerous flooding conditions.
Storm-Surge Floods - This flood type happens primarily as a result of hurricanes. The worst case scenarios for storm surges occur when the surge coincides with the high tide. During a hurricane event, nine out of 10 deaths occur as a result of the storm surge.
Dam and Levee-Failure Floods - While dams and levees are built for flood protection based on a computed risk of occurrence, like any structure, they are susceptible to failure. When a dam or levee floods, the resulting floods can be catastrophic because of the tremendous energy released in a short amount of time.
Debris, Landslide and Mudflow Floods - These flood types are similar to ice floods in that a temporary dam is formed causing upstream water levels to rise. After this temporary debris dam fails, a high energy wave of water is released and travels downstream causing flooding.
Most flood-related deaths are due to flash floods.
Fifty percent of all flash-flood fatalities are vehicle related.
Ninety percent of those who die in hurricanes drown.
Most homeowners insurance policies do not cover damages caused by flooding.