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How Streamflow is Measured
Part 4: Converting stage information to streamflow information

Introduction 1: Measuring stage 2: Discharge measurement 3: Stage-discharge relation 4: Converting stage to streamflow

Most USGS streamgages transmit stage data by satellite to USGS computers where the stage data are used to esti-mate streamflow using the developed stage-discharge relation (rating) (see diagram below). The stage information is routinely reviewed and checked to ensure that the calculated discharge is accurate. In addition, the USGS has quality-control processes in place to ensure the streamflow information being reported across the country has comparable quality and is obtained and analyzed using consistent methods.

Most of the stage and streamflow information produced by the USGS is available in near real time through the National Water Information System (NWIS) World Wide Web site (http://waterdata.usgs.gov/nwis/). In addition to real-time streamgage data, the NWIS Web site also provides access to daily discharges and annual maximum discharges for the period of record for all active and discontinued streamgages operated by the USGS.

A typical stage-discharge relation; here, the discharge of the river is 40 cubic feet per second (ft3/s) when the stage is 3.30 feet (ft). The dots on the curve represent concurrent measurement of stage and discharge.

Streamflow summary

Streamgaging involves obtaining a continuous record of stage, making periodic discharge measurements, establishing and maintaining a relation between the stage and discharge, and applying the stage-discharge relation to the stage record to obtain a continuous record of discharge. The USGS has provided the Nation with consistent, reliable streamflow information for over 115 years. USGS streamflow information is critical for supporting water management, hazard management, environmental research, and infrastructure design. For more information on USGS streamgaging, go to the USGS Web site at http://water.usgs.gov. The National Streamflow Information Program offers more information on this topic., Go to the USGS Office of Surface Water Web site for more information on surface-water activities, and the USGS WaterWatch site gives you current streamflow conditions nationwide or in your area.

Sources and more information


How the stream height (stage) relates to the amount of water flowing in a stream
Real-time USGS streamflow data

Learn about the water cycle, with a diagram in over 60 languages.The water cycle: Streamflow

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Page Last Modified: Friday, 09-Mar-2012 14:21:17 EST