RELATED ECOLOGY PROGRAM
Flooding in Washington State
Floods are the most common and widespread of all natural disasters - except fire. Most U.S. communities can experience some kind of flooding after spring rains, heavy thunderstorms, or winter snow thaws. Floods can be slow or fast-rising but generally develop over a period of days.
Dam failures are potentially the worst flood events. A dam failure is usually the result of neglect, poor design, or structural damage caused by a major event such as an earthquake. When a dam fails, a gigantic quantity of water is suddenly let loose downstream, destroying anything in its path.
In Washington, the primary mechanisms causing a flood situation are:
What is a flash flood?
Flash floods usually result from intense storms dropping large amounts of rain within a brief period. Flash floods occur with little or no warning and can reach full peak in only a few minutes. Central and Eastern Washington are more prone to flash floods than Western Washington.
Floods and flash floods occur in all 50 states. Communities at risk particularly are located in low-lying areas near water, or downstream from a dam.
Where is the greatest flooding risk?
In areas prone to flooding, the Federal Emergency Management Agency (FEMA) provides local communities with flood maps that identify what is known as the “Special Flood Hazard Area” or SFHA. These are areas that experience a 1 percent annual change of flooding. This statistic is somewhat misleading. In Western Washington the actual occurrence of a flood on any river system that drains to the Puget Sound has been roughly every 4.5 years. The Special Flood Hazard Area is regulated under the National Flood Insurance Program (NFIP) for those communities voluntarily joining the program. Local governments implement flood plain management programs that meet or exceed federal and state standards for protecting local residents and businesses from flooding.
Do I live in a flood hazard area?
Ecology’s Coastal Atlas provides a tool that allows people to type their address and find out if they have a home or business that lies in the Special Flood Hazard Area. Note that local communities may have a larger regulated area than the Special Flood Hazard Area. Some communities, for example, may regulate to the highest recorded level of floodwaters for the community, which may exceed the Special Flood Hazard Area.
Washington Flooding History
Washington is one of the most flood-prone states in the nation.
Here are some unique facts:
Floodplain Management in Washington State
Here's some floodplain management history for Washington:
Copyright © Washington State Department of Ecology. See http://www.ecy.wa.gov/copyright.htm