How USGS Measures River Flow

2026-05-01

The United States Geological Survey operates over 8,000 stream gauges across the country, providing real-time data on river flow and water levels. These gauges use a combination of pressure sensors, acoustic doppler current profilers, and traditional current meters to measure discharge. The data is transmitted via satellite every 15 minutes to four hours, depending on the site. Each gauge measures water stage (height) first, then uses a rating curve developed through periodic manual measurements to convert stage to discharge

. This system has been operating since 1889, making it one of the oldest continuous environmental monitoring networks in the world. The data is freely available through the USGS Water Services API and is used for flood forecasting, water supply planning, recreation safety, and scientific research..