Flooded streamgage, Kennebec River at Hallowell, Maine – 01049330. Photo taken after a powerful rainstorm.
Why doesn’t USGS measure gage height from the bottom of the stream?
Streams are like living things and are constantly changing. Sometimes streams erode, becoming deeper, while other times streams deposit sediment, becoming shallower. To understand how those changes can affect streamflow, we need to measure from a reference point that does not change over time, which is why gage datums are chosen to be below the base of a streambed. This means that the gage datum is a uniquely selected reference point for each gage site.
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What does the term "stream stage" mean? What does the term "stream stage" mean?
Stream stage (aka gage height) is an important concept when analyzing how much water is moving in a stream at any given moment. "Stage" is the water level above some arbitrary point in the river and is commonly measured in feet. For example, on a normal day when no rain has fallen for a while, a river might have a stage of 2 feet. If a big storm hits, the river stage could rise to 15 or 20 feet...
Does "stage" tell you how much water is flowing in a stream? Does "stage" tell you how much water is flowing in a stream?
Not directly. You cannot say that because a stream rises (doubles) from a 10-foot stage to a 20-foot stage that the amount of flowing water also doubles. Think of a cereal bowl with a rounded bottom. Pour one inch of milk in it. It doesn't take much milk to make it up to the one inch level because the bowl is at its narrowest near the bottom. Now, pour in milk until it is two inches deep -- it...
How is a rating curve used to convert gage height into streamflow? How is a rating curve used to convert gage height into streamflow?
In order to convert gage height (or "stage", usually expressed as feet) into streamflow (or "discharge", usually expressed as cubic feet per second), USGS hydrographers must establish a relationship between them. This stage-discharge relationship is called a rating curve. It’s developed by making frequent manual discrete discharge measurements at stream gaging stations. The rating curve depends on...
Sometimes the USGS real-time stage data seems too high (or too low). Are the USGS data inaccurate? Sometimes the USGS real-time stage data seems too high (or too low). Are the USGS data inaccurate?
There can be occasional equipment or database problems where erroneous data are reported for short periods of time until corrections can be made. This is why it is important to look at a record of streamflow (like the 7-day hydrograph plots) rather than a single point in time. However, most of the time the USGS has a high level of confidence in its real-time stage data. During low streamflow...
Why are there sometimes differences between USGS and National Weather Service river stages? Why are there sometimes differences between USGS and National Weather Service river stages?
At some USGS streamgage installations, NOAA’s National Weather Service (NWS) maintains a separate stage sensor that is serviced by NWS technicians. Calibration of any sensing device can occasionally drift from a "true" value, so there might be differences between USGS and NWS data reports. USGS personnel visit installations on an interval of 6 weeks or less to maintain equipment and make required...
Flooded streamgage
Flooded streamgage, Kennebec River at Hallowell, Maine – 01049330. Photo taken after a powerful rainstorm.
Karli Rogers collecting gage height data
This photo shows Karli Rogers gathering gage height data to support research on a headwater stream gage in Shenandoah National Park in Virginia.
This photo shows Karli Rogers gathering gage height data to support research on a headwater stream gage in Shenandoah National Park in Virginia.
Cleaning and inspecting water height reference staff at streamgage
Cleaning and inspecting water height reference staff at streamgageUSGS hydrologist Adam Birken cleans and inspects the water height reference staff at the USGS streamgage site on the South Fork of the Ogden River near Hunstville, Utah. This streamgage has been monitoring water levels and flow since March 21, 1921, making it one of 25 centennial gauges in Utah.
Cleaning and inspecting water height reference staff at streamgage
Cleaning and inspecting water height reference staff at streamgageUSGS hydrologist Adam Birken cleans and inspects the water height reference staff at the USGS streamgage site on the South Fork of the Ogden River near Hunstville, Utah. This streamgage has been monitoring water levels and flow since March 21, 1921, making it one of 25 centennial gauges in Utah.
How USGS Streamgages Work
This video explains how streamgages are used to measure the height and flow, or speed, of streams. By monitoring the height and flow of streams, the people who manage water infrastructure can have advanced noted of when the water is rising and how fast it’s coming.
This video explains how streamgages are used to measure the height and flow, or speed, of streams. By monitoring the height and flow of streams, the people who manage water infrastructure can have advanced noted of when the water is rising and how fast it’s coming.
USGS staff gage measuring the height of the water in the Carson River
USGS staff gage measuring the height of the water in the Carson RiverUSGS staff gage (ruler) measuring the height of the water, on the Carson River, near Brunswick Canyon, Nevada.
USGS staff gage measuring the height of the water in the Carson River
USGS staff gage measuring the height of the water in the Carson RiverUSGS staff gage (ruler) measuring the height of the water, on the Carson River, near Brunswick Canyon, Nevada.
USGS streamgage measures flooding in the lower Trinity River
USGS streamgage measures flooding in the lower Trinity RiverA USGS streamgage measures flooding in the lower Trinity River, Texas.
USGS streamgage measures flooding in the lower Trinity River
USGS streamgage measures flooding in the lower Trinity RiverA USGS streamgage measures flooding in the lower Trinity River, Texas.
USGS Red River of the North at Fargo Streamgage
Water level measurement from the USGS Red River of the North at Fargo streamgage in downtown Fargo, ND. The water level peaked at around 39 feet at this streamgage on April 9. Real-time water level and streamflow data from this gage can be accessed online.
Water level measurement from the USGS Red River of the North at Fargo streamgage in downtown Fargo, ND. The water level peaked at around 39 feet at this streamgage on April 9. Real-time water level and streamflow data from this gage can be accessed online.
Streamgages: The Silent Superhero
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.
Related
What does the term "stream stage" mean? What does the term "stream stage" mean?
Stream stage (aka gage height) is an important concept when analyzing how much water is moving in a stream at any given moment. "Stage" is the water level above some arbitrary point in the river and is commonly measured in feet. For example, on a normal day when no rain has fallen for a while, a river might have a stage of 2 feet. If a big storm hits, the river stage could rise to 15 or 20 feet...
Does "stage" tell you how much water is flowing in a stream? Does "stage" tell you how much water is flowing in a stream?
Not directly. You cannot say that because a stream rises (doubles) from a 10-foot stage to a 20-foot stage that the amount of flowing water also doubles. Think of a cereal bowl with a rounded bottom. Pour one inch of milk in it. It doesn't take much milk to make it up to the one inch level because the bowl is at its narrowest near the bottom. Now, pour in milk until it is two inches deep -- it...
How is a rating curve used to convert gage height into streamflow? How is a rating curve used to convert gage height into streamflow?
In order to convert gage height (or "stage", usually expressed as feet) into streamflow (or "discharge", usually expressed as cubic feet per second), USGS hydrographers must establish a relationship between them. This stage-discharge relationship is called a rating curve. It’s developed by making frequent manual discrete discharge measurements at stream gaging stations. The rating curve depends on...
Sometimes the USGS real-time stage data seems too high (or too low). Are the USGS data inaccurate? Sometimes the USGS real-time stage data seems too high (or too low). Are the USGS data inaccurate?
There can be occasional equipment or database problems where erroneous data are reported for short periods of time until corrections can be made. This is why it is important to look at a record of streamflow (like the 7-day hydrograph plots) rather than a single point in time. However, most of the time the USGS has a high level of confidence in its real-time stage data. During low streamflow...
Why are there sometimes differences between USGS and National Weather Service river stages? Why are there sometimes differences between USGS and National Weather Service river stages?
At some USGS streamgage installations, NOAA’s National Weather Service (NWS) maintains a separate stage sensor that is serviced by NWS technicians. Calibration of any sensing device can occasionally drift from a "true" value, so there might be differences between USGS and NWS data reports. USGS personnel visit installations on an interval of 6 weeks or less to maintain equipment and make required...
Karli Rogers collecting gage height data
This photo shows Karli Rogers gathering gage height data to support research on a headwater stream gage in Shenandoah National Park in Virginia.
This photo shows Karli Rogers gathering gage height data to support research on a headwater stream gage in Shenandoah National Park in Virginia.
Cleaning and inspecting water height reference staff at streamgage
Cleaning and inspecting water height reference staff at streamgageUSGS hydrologist Adam Birken cleans and inspects the water height reference staff at the USGS streamgage site on the South Fork of the Ogden River near Hunstville, Utah. This streamgage has been monitoring water levels and flow since March 21, 1921, making it one of 25 centennial gauges in Utah.
Cleaning and inspecting water height reference staff at streamgage
Cleaning and inspecting water height reference staff at streamgageUSGS hydrologist Adam Birken cleans and inspects the water height reference staff at the USGS streamgage site on the South Fork of the Ogden River near Hunstville, Utah. This streamgage has been monitoring water levels and flow since March 21, 1921, making it one of 25 centennial gauges in Utah.
How USGS Streamgages Work
This video explains how streamgages are used to measure the height and flow, or speed, of streams. By monitoring the height and flow of streams, the people who manage water infrastructure can have advanced noted of when the water is rising and how fast it’s coming.
This video explains how streamgages are used to measure the height and flow, or speed, of streams. By monitoring the height and flow of streams, the people who manage water infrastructure can have advanced noted of when the water is rising and how fast it’s coming.
USGS staff gage measuring the height of the water in the Carson River
USGS staff gage measuring the height of the water in the Carson RiverUSGS staff gage (ruler) measuring the height of the water, on the Carson River, near Brunswick Canyon, Nevada.
USGS staff gage measuring the height of the water in the Carson River
USGS staff gage measuring the height of the water in the Carson RiverUSGS staff gage (ruler) measuring the height of the water, on the Carson River, near Brunswick Canyon, Nevada.
USGS streamgage measures flooding in the lower Trinity River
USGS streamgage measures flooding in the lower Trinity RiverA USGS streamgage measures flooding in the lower Trinity River, Texas.
USGS streamgage measures flooding in the lower Trinity River
USGS streamgage measures flooding in the lower Trinity RiverA USGS streamgage measures flooding in the lower Trinity River, Texas.
USGS Red River of the North at Fargo Streamgage
Water level measurement from the USGS Red River of the North at Fargo streamgage in downtown Fargo, ND. The water level peaked at around 39 feet at this streamgage on April 9. Real-time water level and streamflow data from this gage can be accessed online.
Water level measurement from the USGS Red River of the North at Fargo streamgage in downtown Fargo, ND. The water level peaked at around 39 feet at this streamgage on April 9. Real-time water level and streamflow data from this gage can be accessed online.
Streamgages: The Silent Superhero
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.
Updated Date: July 9, 2025