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The term "100-year flood" is used to describe the recurrence interval of floods. The 100-year recurrence interval means that a flood of that magnitude has a one percent chance of occurring in any given year. In other words, the chances that a river will flow as high as the 100-year flood stage this year is 1 in 100. Statistically, each year begins with the same 1-percent chance that a 100-year event will occur.
Learn more:
Climate variability (dry cycles to wet cycles) and land-use change play a significant role, but there is a large amount of uncertainty around the flood quantile estimates (the value of discharge corresponding to the 100-year flood), particularly if there isn’t a long record of observed data at a stream location. Learn more: The 100-Year Flood The 100-Year Flood--It's All About Chance
Flood predictions require several types of data: The amount of rainfall occurring on a real-time basis. The rate of change in river stage on a real-time basis, which can help indicate the severity and immediacy of the threat. Knowledge about the type of storm producing the moisture, such as duration, intensity and areal extent, which can be valuable for determining possible severity of the...
It comes down to a number of factors, including the pattern of movement of the rainstorm in each particular watershed, the conditions of the soil and plant matter in the watershed, and the timing of the rainstorm in one watershed versus other watersheds. For example, if the ground is already saturated before a rainstorm, much of the rain will run off into streams, but if the ground is dry, it will...
There are two basic types of floods: flash floods and the more widespread river floods. Flash floods generally cause greater loss of life and river floods generally cause greater loss of property. A flash flood occurs when runoff from excessive rainfall causes a rapid rise in the water height (stage) of a stream or normally-dry channel. Flash floods are more common in areas with a dry climate and...
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.
FEMA is the official public source for flood maps for insurance purposes: FEMA’s Flood Map Service Center FEMA’s National Flood Hazard Layer NOAA is responsible for producing flood forecast maps that combine precipitation data with USGS streamflow data: NWS - National Water Prediction Service: River forecasts and long range flood outlook Coastal Inundation Dashboard: Real-time and historical...
The amount of water corresponding to a 100-year flood, a 500-year flood, or a 1,000-year flood is known as a "flood quantile." For instance, on a given river, the flood quantile corresponding to the 50-year flood might be 10,000 cubic feet per second (cfs) and the flood quantile corresponding to the 100-year flood might be 15,000 cfs. The estimates of the flood quantiles are calculated using...
USGS water expert Emma Spicer uses specialized wading rod to measure the height of floodwaters over a submerged bridge on Cedar Creek at Highway 1442 near Shepherdsville, Kentucky on April 7, 2025.
USGS water expert Emma Spicer uses specialized wading rod to measure the height of floodwaters over a submerged bridge on Cedar Creek at Highway 1442 near Shepherdsville, Kentucky on April 7, 2025.
A building lifted from its foundation by floodwater from Extratropical Typhoon Merbok is trapped under a bridge in Nome, Alaska.
A building lifted from its foundation by floodwater from Extratropical Typhoon Merbok is trapped under a bridge in Nome, Alaska.
100-Year Flood - It's All About Chance poster image
100-Year Flood - It's All About Chance poster image
Hurricane Florence (2018) modeling: The coupled model captures the stages of compound flooding in the Cape Fear River Estuary starting with swell from offshore, followed by storm surge from the ocean side, later transitioning to flooding from land side with the storm water runoff because of rain.
Hurricane Florence (2018) modeling: The coupled model captures the stages of compound flooding in the Cape Fear River Estuary starting with swell from offshore, followed by storm surge from the ocean side, later transitioning to flooding from land side with the storm water runoff because of rain.
USGS hydrographer measuring streamflow using a handheld Acoustic Doppler Velocimeter in fast moving floodwater Cajon Creek near Keenbrook, California.
USGS hydrographer measuring streamflow using a handheld Acoustic Doppler Velocimeter in fast moving floodwater Cajon Creek near Keenbrook, California.
Flooding costs the United States more than $7 billion per year and claims more than 90 lives annually. During the Spring and Summer of 2011, the central U.S. experienced epic flooding, while Hurricane Irene followed by Tropical Storm Lee caused severe flooding in the east and northeastern U.S, setting numerous flood records at USGS streamgages. Dr.
Flooding costs the United States more than $7 billion per year and claims more than 90 lives annually. During the Spring and Summer of 2011, the central U.S. experienced epic flooding, while Hurricane Irene followed by Tropical Storm Lee caused severe flooding in the east and northeastern U.S, setting numerous flood records at USGS streamgages. Dr.
Gagehouse at 06225500 Wind River near Crowheart WY right before it washed away.
Jul 01 2011; 13,900 ft3/s
Gagehouse at 06225500 Wind River near Crowheart WY right before it washed away.
Jul 01 2011; 13,900 ft3/s
Whether you drink water from your tap, use electricity or canoe down your local river, chances are you benefit from USGS streamgage information. So what is a streamgage and what does it do for you? This CoreCast episode gives you the inside scoop on your silent superhero.
Transcript and captions available soon.
Whether you drink water from your tap, use electricity or canoe down your local river, chances are you benefit from USGS streamgage information. So what is a streamgage and what does it do for you? This CoreCast episode gives you the inside scoop on your silent superhero.
Transcript and captions available soon.
Epic Flooding in Georgia, 2009
Metropolitan Atlanta—September 2009 Floods
Epic Flooding in Georgia, 2009
Metropolitan Atlanta—September 2009 Floods
We talk to Bob Holmes about some of the recent flooding events occuring in the Midwest, how does a 500-year flood occur twice in 15 years, and what do the recent events have in store for folks downriver.
We talk to Bob Holmes about some of the recent flooding events occuring in the Midwest, how does a 500-year flood occur twice in 15 years, and what do the recent events have in store for folks downriver.
Flooded neighborhood near 12th Ave and 4th Street
Flooded neighborhood near 12th Ave and 4th Street
Flooded neighborhood near Wilson Ave. SW and Hamilton Street SW
Flooded neighborhood near Wilson Ave. SW and Hamilton Street SW
Listen to hear the answer.
Climate variability (dry cycles to wet cycles) and land-use change play a significant role, but there is a large amount of uncertainty around the flood quantile estimates (the value of discharge corresponding to the 100-year flood), particularly if there isn’t a long record of observed data at a stream location. Learn more: The 100-Year Flood The 100-Year Flood--It's All About Chance
Flood predictions require several types of data: The amount of rainfall occurring on a real-time basis. The rate of change in river stage on a real-time basis, which can help indicate the severity and immediacy of the threat. Knowledge about the type of storm producing the moisture, such as duration, intensity and areal extent, which can be valuable for determining possible severity of the...
It comes down to a number of factors, including the pattern of movement of the rainstorm in each particular watershed, the conditions of the soil and plant matter in the watershed, and the timing of the rainstorm in one watershed versus other watersheds. For example, if the ground is already saturated before a rainstorm, much of the rain will run off into streams, but if the ground is dry, it will...
There are two basic types of floods: flash floods and the more widespread river floods. Flash floods generally cause greater loss of life and river floods generally cause greater loss of property. A flash flood occurs when runoff from excessive rainfall causes a rapid rise in the water height (stage) of a stream or normally-dry channel. Flash floods are more common in areas with a dry climate and...
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.
FEMA is the official public source for flood maps for insurance purposes: FEMA’s Flood Map Service Center FEMA’s National Flood Hazard Layer NOAA is responsible for producing flood forecast maps that combine precipitation data with USGS streamflow data: NWS - National Water Prediction Service: River forecasts and long range flood outlook Coastal Inundation Dashboard: Real-time and historical...
The amount of water corresponding to a 100-year flood, a 500-year flood, or a 1,000-year flood is known as a "flood quantile." For instance, on a given river, the flood quantile corresponding to the 50-year flood might be 10,000 cubic feet per second (cfs) and the flood quantile corresponding to the 100-year flood might be 15,000 cfs. The estimates of the flood quantiles are calculated using...
USGS water expert Emma Spicer uses specialized wading rod to measure the height of floodwaters over a submerged bridge on Cedar Creek at Highway 1442 near Shepherdsville, Kentucky on April 7, 2025.
USGS water expert Emma Spicer uses specialized wading rod to measure the height of floodwaters over a submerged bridge on Cedar Creek at Highway 1442 near Shepherdsville, Kentucky on April 7, 2025.
A building lifted from its foundation by floodwater from Extratropical Typhoon Merbok is trapped under a bridge in Nome, Alaska.
A building lifted from its foundation by floodwater from Extratropical Typhoon Merbok is trapped under a bridge in Nome, Alaska.
100-Year Flood - It's All About Chance poster image
100-Year Flood - It's All About Chance poster image
Hurricane Florence (2018) modeling: The coupled model captures the stages of compound flooding in the Cape Fear River Estuary starting with swell from offshore, followed by storm surge from the ocean side, later transitioning to flooding from land side with the storm water runoff because of rain.
Hurricane Florence (2018) modeling: The coupled model captures the stages of compound flooding in the Cape Fear River Estuary starting with swell from offshore, followed by storm surge from the ocean side, later transitioning to flooding from land side with the storm water runoff because of rain.
USGS hydrographer measuring streamflow using a handheld Acoustic Doppler Velocimeter in fast moving floodwater Cajon Creek near Keenbrook, California.
USGS hydrographer measuring streamflow using a handheld Acoustic Doppler Velocimeter in fast moving floodwater Cajon Creek near Keenbrook, California.
Flooding costs the United States more than $7 billion per year and claims more than 90 lives annually. During the Spring and Summer of 2011, the central U.S. experienced epic flooding, while Hurricane Irene followed by Tropical Storm Lee caused severe flooding in the east and northeastern U.S, setting numerous flood records at USGS streamgages. Dr.
Flooding costs the United States more than $7 billion per year and claims more than 90 lives annually. During the Spring and Summer of 2011, the central U.S. experienced epic flooding, while Hurricane Irene followed by Tropical Storm Lee caused severe flooding in the east and northeastern U.S, setting numerous flood records at USGS streamgages. Dr.
Gagehouse at 06225500 Wind River near Crowheart WY right before it washed away.
Jul 01 2011; 13,900 ft3/s
Gagehouse at 06225500 Wind River near Crowheart WY right before it washed away.
Jul 01 2011; 13,900 ft3/s
Whether you drink water from your tap, use electricity or canoe down your local river, chances are you benefit from USGS streamgage information. So what is a streamgage and what does it do for you? This CoreCast episode gives you the inside scoop on your silent superhero.
Transcript and captions available soon.
Whether you drink water from your tap, use electricity or canoe down your local river, chances are you benefit from USGS streamgage information. So what is a streamgage and what does it do for you? This CoreCast episode gives you the inside scoop on your silent superhero.
Transcript and captions available soon.
Epic Flooding in Georgia, 2009
Metropolitan Atlanta—September 2009 Floods
Epic Flooding in Georgia, 2009
Metropolitan Atlanta—September 2009 Floods
We talk to Bob Holmes about some of the recent flooding events occuring in the Midwest, how does a 500-year flood occur twice in 15 years, and what do the recent events have in store for folks downriver.
We talk to Bob Holmes about some of the recent flooding events occuring in the Midwest, how does a 500-year flood occur twice in 15 years, and what do the recent events have in store for folks downriver.
Flooded neighborhood near 12th Ave and 4th Street
Flooded neighborhood near 12th Ave and 4th Street
Flooded neighborhood near Wilson Ave. SW and Hamilton Street SW
Flooded neighborhood near Wilson Ave. SW and Hamilton Street SW
Listen to hear the answer.
