Nevada Water Science Center

Northern Nevada Floods 2017

From a Stream to the Web...How we measure flood waters

During storms, USGS field crews travel to many sites along rivers and streams to measure streamflow. What do we mean exactly when we say we measure streamflow?

  1. We determine the location that measurements will be taken, which is called a cross section. The cross section is then divided into numerous subsections.
  2. The width and the depth of each subsection is measured to calculate the area.
  3. The water velocity, or speed, within each subsection is measured using a current meter or Acoustic Doppler Current Profiler (ADCP).
  4. Area and velocity are multiplied together to determine the discharge of each subsection. The subsection discharges are added together for the total discharge.

Discharge is the amount of water passing a particular point in a stream for a certain period of time. We usually use cubic feet per second (cfs) to describe the discharge in a stream.

Current Meters

Bridge Measurements


Real-Time Data

For many streams, USGS uses a streamgage to determine streamflow. A streamgage uses a pressure transducer or floats inside a stilling well to measure river stage. A data logger, inside the gagehouse, stores the river stage data until the data is transmitted back to the USGS office. Data is transmitted back to the USGS office every hour. At the USGS office, a rating curve relating stage to streamflow is applied to determine discharge. The streamflow measurements described above are used to define the rating curve. The stage and discharge measurements are both then sent to NWISweb.

Databases and Web Pages

All USGS data is stored in the USGS National Water Information System (NWIS). Our stage and streamflow data are available through NWISweb, a web interface to NWIS. You can also access NWIS data through the NWIS mapper which provides a map interface to find data.

Data available on NWISweb
  • Current Conditions: Sites with real-time or recent surface-water, groundwater, or water-quality data
  • Site Information: Descriptive information for all sites with links to all available water data for individual sites
  • Surface Water: Historical Observations, Daily Data, Statistics, Peak-Flow Data, and Field Measurements
  • Ground Water: Historical Observations, Daily Data, Statistics, and Field Measurements
  • Water Quality: Historical Observations, Daily Data, Statistics, and Field/Lab Samples
  • Water Use: State Data

Want to know more?

Streamgages: The Silent Superhero

USGS has produced a short video about what a streamgage is and what it does for you.

Streamflow, groundwater, and water-quality monitoring by USGS Nevada Water Science Center

U.S. Geological Survey Fact Sheet 2013-3004

Streamflow data are available on the Nevada WSC web page ( in real time. Longterm data (greater than 5 years of continuous record) provide baseline data that can be used to analyze peak, mean, and low flows. Data can also be used to determine flood frequency...

How does a U.S. Geological Survey streamgage work?

U.S. Geological Survey Fact Sheet 2011-3001

Information on the flow of rivers and streams is a vital national asset that safeguards lives, protects property, and ensures adequate water supplies for the future...

U.S. Geological Survey Streamgaging

U.S. Geological Survey Fact Sheet 2005-3131

The U.S. Geological Survey (USGS) started its first streamgage in 1889 on the Rio Grande River in New Mexico to help determine if there was adequate water for irrigation purposes to encourage new development and western expansion...