What is a 1,000-year flood?
The term “1,000-year flood” means that, statistically speaking, a flood of that magnitude (or greater) has a 1 in 1,000 chance of occurring in any given year. In terms of probability, the 1,000-year flood has a 0.1% chance of happening in any given year.
These statistical values are based on observed data.
Related Content
Why do the values for the 100-year flood seem to change with every flood?
Does an increase in the 100-year flood estimate originate from climate or land-use change?
How can a 1,000-year rainfall not result in a 1,000-year flood?
We had a "100-year flood" two years in a row. How can that be?
Where can I find flood maps?
How are floods predicted?
What are the two types of floods?
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Fragmented Patterns Seen in the Recent History of U.S. Floods
Some regional trends; no widespread national pattern
Measuring streamflow in fast moving floodwater.
USGS hydrographer measuring streamflow using a handheld Acoustic Doppler Velocimeter in fast moving floodwater Cajon Creek near Keenbrook, California.
NGS Aerial Imagery of Louisiana Flooding
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The Anatomy of Floods: The Causes and Development of 2011's Epic Flood Events
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Flood Waters Take USGS Streamgage Wind River near Crowheart, WY
Gagehouse at 06225500 Wind River near Crowheart WY right before it washed away.
Jul 01 2011; 13,900 ft3/s
Streamgages: The Silent Superhero
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Transcript and captions available soon.
Interview: 2009 Fargo, ND Flooding
Interview with USGS crews regarding the 2009 flooding events in Fargo, ND.
Flooding in Finchfield, IA
Flooding of a house
St. John River at Ft. Kent, Maine Flood 2008
Understanding the forces that influence major floods can help inform the design of more resilient infrastructure. Image shows a major flood on the St. John River on the border of Maine, United States and New Brunswick, Canada, April 29, 2008. This site was part of the study. USGS Public Domain.
A photo of floodwaters reaching up to a street sign in Texas
A photo of floodwaters reaching up to a street sign in Texas.
A USGS crew prepares to measure Hurricane Harvey floodwaters
A USGS crew prepares to measure Hurricane Harvey floodwaters off of a bridge. Photo by Cassi Crow, USGS.