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 the physical characteristics of the stream channel and floodplain, and will vary over time at almost every station. There are often subtle changes to a natural stream channel, such as the growth of aquatic vegetation in the summer, frequent shifting of a sand-bed stream bottom, catastrophic changes due to floods, or man-made changes such as construction of a bridge. These changes might require only minor or temporary adjustments to the rating curve, or they could require the development of a new one.
Provisional rating curves for many USGS streamgages are posted in WaterWatch. Place your cursor over the site of interest and left-click. That generates a pop-up window with a rating tab on the far right. Or if you know the site number for a USGS streamgage, plug it into the Customized Rating Curve Builder. For more information about site-specific rating curves, contact the USGS Water Science Center that manages the site.
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Is there a way to get alerts about streamflow conditions?
Yes! The USGS offers two services: WaterAlert - automated emails or text messages are sent to you whenever certain parameters (that you define) are exceeded at one of our gaging stations. WaterNow - Send an email or text message to WaterNow@usgs.gov containing the USGS Site Number of the gage you want to query (optionally add parameter codes to customize your query). You will receive an automated...
What does the term "stream stage" mean?
Stream stage 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, sometimes very...
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...
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...
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...
Where can I get real-time and historical streamflow information?
The best starting point for USGS streamflow data is the interactive National Water Information System (NWIS): Mapper website. Zoom in to your area of interest or use the search options in the left navigation window. The map displays active surface-water sites by default, but you can change the type of water site (surface-water, groundwater, springs, atmospheric) and select to show inactive sites...
Why does the USGS use the spelling "gage" instead of "gauge"?
The spelling of “gage” is part of our very rich USGS history. In 1888, USGS Director John Wesley Powell met a very forward-thinking graduate student named Frederick Haynes Newell. Powell was so impressed that he made Newell the first full-time appointee to the new Irrigation Survey, which was created to investigate the potential for dams and canals in the western United States.At that time, there...
Why might USGS streamflow data be revised?
Real-time USGS streamflow data are PROVISIONAL, meaning that the data have not been reviewed or edited. These data might be subject to significant change and are not official until reviewed and approved by the USGS. Real-time streamflow data can be affected by: backwater from ice or debris such as log jams algae and aquatic growth in the stream sediment movement malfunction of recording equipment...
Related Content
- FAQ
Is there a way to get alerts about streamflow conditions?
Yes! The USGS offers two services: WaterAlert - automated emails or text messages are sent to you whenever certain parameters (that you define) are exceeded at one of our gaging stations. WaterNow - Send an email or text message to WaterNow@usgs.gov containing the USGS Site Number of the gage you want to query (optionally add parameter codes to customize your query). You will receive an automated...
What does the term "stream stage" mean?
Stream stage 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, sometimes very...
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...
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...
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...
Where can I get real-time and historical streamflow information?
The best starting point for USGS streamflow data is the interactive National Water Information System (NWIS): Mapper website. Zoom in to your area of interest or use the search options in the left navigation window. The map displays active surface-water sites by default, but you can change the type of water site (surface-water, groundwater, springs, atmospheric) and select to show inactive sites...
Why does the USGS use the spelling "gage" instead of "gauge"?
The spelling of “gage” is part of our very rich USGS history. In 1888, USGS Director John Wesley Powell met a very forward-thinking graduate student named Frederick Haynes Newell. Powell was so impressed that he made Newell the first full-time appointee to the new Irrigation Survey, which was created to investigate the potential for dams and canals in the western United States.At that time, there...
Why might USGS streamflow data be revised?
Real-time USGS streamflow data are PROVISIONAL, meaning that the data have not been reviewed or edited. These data might be subject to significant change and are not official until reviewed and approved by the USGS. Real-time streamflow data can be affected by: backwater from ice or debris such as log jams algae and aquatic growth in the stream sediment movement malfunction of recording equipment...
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