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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 actual data collected at a site.
For a particular river, the USGS collects data over time, determines the largest flood in each year, and then calculate statistical data for that river. The more years of data available, the more accurate the estimates for the various flood quantiles.
As more years of data become available, the estimates become more refined, which can result in revisions to the quantiles.
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...
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...
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 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.
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...
USGS water expert Conner Langley measures flood water speed and height at Cumberland River in Barbourville, KY on February 17. He holds a radio in his left hand to stay in contact with colleagues for safety and to relay water flow measurements. This Cumberland River streamgage is funded by the U.S.
USGS water expert Conner Langley measures flood water speed and height at Cumberland River in Barbourville, KY on February 17. He holds a radio in his left hand to stay in contact with colleagues for safety and to relay water flow measurements. This Cumberland River streamgage is funded by the U.S.
USGS water data expert Garret Welsh measures water flow in the pouring rain at the Straight River near Faribault, Minnesota. This measurement recorded the 6th highest flow in the station's 59-year history, highlighting the severity of current flood conditions. Such data is crucial for emergency managers and forecasters to protect communities at risk.
USGS water data expert Garret Welsh measures water flow in the pouring rain at the Straight River near Faribault, Minnesota. This measurement recorded the 6th highest flow in the station's 59-year history, highlighting the severity of current flood conditions. Such data is crucial for emergency managers and forecasters to protect communities at risk.
This USGS webcam footage shows the Kennebec River in Augusta, Maine, flooding after a large coastal storm hit much of the East Coast and battered New England with heavy rains and winds. USGS image.
This USGS webcam footage shows the Kennebec River in Augusta, Maine, flooding after a large coastal storm hit much of the East Coast and battered New England with heavy rains and winds. USGS image.
USGS scientist Brad Slaugh taking measurements following a flash flood event in Hildale, Utah.
USGS scientist Brad Slaugh taking measurements following a flash flood event in Hildale, Utah.
Devastation from the 1913 flood is shown primarily through photographs taken during the March 1913 flood. In the aftermath of the 1913 flood, State and Federal funds were allocated for the installation of a streamgage network to monitor the water level and flow of Ohio's rivers and streams.
Devastation from the 1913 flood is shown primarily through photographs taken during the March 1913 flood. In the aftermath of the 1913 flood, State and Federal funds were allocated for the installation of a streamgage network to monitor the water level and flow of Ohio's rivers and streams.
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.
Devastating floods across much of the U.S. were severe and unrelenting during the spring and summer of 2011. When floods happen, USGS crews are among the first-responders.
Devastating floods across much of the U.S. were severe and unrelenting during the spring and summer of 2011. When floods happen, USGS crews are among the first-responders.
USGS hydrographer Jerrod Wheeler (in cablecar) measures flood flows right before the gagehouse washes away.
06225500 Wind River near Crowheart, WY: Jul 01 2011; 13,900 ft3/s
USGS hydrographer Jerrod Wheeler (in cablecar) measures flood flows right before the gagehouse washes away.
06225500 Wind River near Crowheart, WY: Jul 01 2011; 13,900 ft3/s
Releases of 80,000 cubic feet per second from Oahe Dam near Pierre, SD, on May 27, 2011, during 2011 Missouri River flood.
Releases of 80,000 cubic feet per second from Oahe Dam near Pierre, SD, on May 27, 2011, during 2011 Missouri River flood.
Flooding of a house
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.
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 flash flood on the Colorado River in Grand Canyon, at the Monument Creek debris fan, at Granite Rapid. River rafters, parked far enough upstream to be safe from the flash flood, observe from a high rock and scout potential changes to Granite Rapid. Photo by Jeff Behan.
A flash flood on the Colorado River in Grand Canyon, at the Monument Creek debris fan, at Granite Rapid. River rafters, parked far enough upstream to be safe from the flash flood, observe from a high rock and scout potential changes to Granite Rapid. Photo by Jeff Behan.
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...
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...
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 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.
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...
USGS water expert Conner Langley measures flood water speed and height at Cumberland River in Barbourville, KY on February 17. He holds a radio in his left hand to stay in contact with colleagues for safety and to relay water flow measurements. This Cumberland River streamgage is funded by the U.S.
USGS water expert Conner Langley measures flood water speed and height at Cumberland River in Barbourville, KY on February 17. He holds a radio in his left hand to stay in contact with colleagues for safety and to relay water flow measurements. This Cumberland River streamgage is funded by the U.S.
USGS water data expert Garret Welsh measures water flow in the pouring rain at the Straight River near Faribault, Minnesota. This measurement recorded the 6th highest flow in the station's 59-year history, highlighting the severity of current flood conditions. Such data is crucial for emergency managers and forecasters to protect communities at risk.
USGS water data expert Garret Welsh measures water flow in the pouring rain at the Straight River near Faribault, Minnesota. This measurement recorded the 6th highest flow in the station's 59-year history, highlighting the severity of current flood conditions. Such data is crucial for emergency managers and forecasters to protect communities at risk.
This USGS webcam footage shows the Kennebec River in Augusta, Maine, flooding after a large coastal storm hit much of the East Coast and battered New England with heavy rains and winds. USGS image.
This USGS webcam footage shows the Kennebec River in Augusta, Maine, flooding after a large coastal storm hit much of the East Coast and battered New England with heavy rains and winds. USGS image.
USGS scientist Brad Slaugh taking measurements following a flash flood event in Hildale, Utah.
USGS scientist Brad Slaugh taking measurements following a flash flood event in Hildale, Utah.
Devastation from the 1913 flood is shown primarily through photographs taken during the March 1913 flood. In the aftermath of the 1913 flood, State and Federal funds were allocated for the installation of a streamgage network to monitor the water level and flow of Ohio's rivers and streams.
Devastation from the 1913 flood is shown primarily through photographs taken during the March 1913 flood. In the aftermath of the 1913 flood, State and Federal funds were allocated for the installation of a streamgage network to monitor the water level and flow of Ohio's rivers and streams.
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.
Devastating floods across much of the U.S. were severe and unrelenting during the spring and summer of 2011. When floods happen, USGS crews are among the first-responders.
Devastating floods across much of the U.S. were severe and unrelenting during the spring and summer of 2011. When floods happen, USGS crews are among the first-responders.
USGS hydrographer Jerrod Wheeler (in cablecar) measures flood flows right before the gagehouse washes away.
06225500 Wind River near Crowheart, WY: Jul 01 2011; 13,900 ft3/s
USGS hydrographer Jerrod Wheeler (in cablecar) measures flood flows right before the gagehouse washes away.
06225500 Wind River near Crowheart, WY: Jul 01 2011; 13,900 ft3/s
Releases of 80,000 cubic feet per second from Oahe Dam near Pierre, SD, on May 27, 2011, during 2011 Missouri River flood.
Releases of 80,000 cubic feet per second from Oahe Dam near Pierre, SD, on May 27, 2011, during 2011 Missouri River flood.
Flooding of a house
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.
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 flash flood on the Colorado River in Grand Canyon, at the Monument Creek debris fan, at Granite Rapid. River rafters, parked far enough upstream to be safe from the flash flood, observe from a high rock and scout potential changes to Granite Rapid. Photo by Jeff Behan.
A flash flood on the Colorado River in Grand Canyon, at the Monument Creek debris fan, at Granite Rapid. River rafters, parked far enough upstream to be safe from the flash flood, observe from a high rock and scout potential changes to Granite Rapid. Photo by Jeff Behan.