USGS - science for a changing world

The USGS Water Science School

How the U.S. Geological Survey monitors water

There are many pieces of equipment, both mechanical and electronic, that are installed at stream-monitoring sites all around the world to measure, record, and transmit both water-quantity and water-quality information. The U.S. Geological Survey (USGS) monitors "real-time" streamflow and water-quality conditions for thousands of streams nationwide.

 Uses of streamflow information.
Description of the USGS real-time streamflow system. (new window)

The job of the water scientist

USGS hydrologist taking a water quality sample.Long-term monitoring of water resources requires knowledge, skills, and commitment developed over decades by the men and women of USGS. USGS streamgagers and hydrologists must develop and follow precise scientific procedures to assure the quality of water measurements and to properly interpret the meaning of water data. High-quality data is essential for the wise management and use of water resources. Technological advances have improved the amount and timing of data, and made stream monitoring more complex, but these have not reduced the need to physically measure the stream over the range of possible flows, particularly during floods, whenever they occur.

Stream-stage monitoring instrumentation

Picture showing one type of USGS gage house which houses a stilling well (a vertical pipe), and measurement and data-transmission instruments. This picture shows one type of USGS gage structure which is attached to a stilling well (the vertical pipe), and the shelter contains measurement and data-transmission instruments. Equipment in the gage house continuously measure stream height (stage) every 15 minutes. Stilling wells are used at locations where they can built next to the stream, but other systems monitoring water pressure can be used in different situations.
 Find out more.

Picture showing the box on top of the stilling well that holds the measuring wire and automated data logger to record stream stages. The box on top of the pipe contains a measuring instrument (data logger) that has a pulley with a metal tape holding a float at one end. As the water in the stream rises and falls, the water in the vertical metal pipe also moves and the float on the wire goes up and down with the water level. As the wire moves, the pulley turns, which changes the stream-stage (gage height) reading. The stream-stage readings are recorded by the data logger. Peachtree Creek has a solar-powered GOES satellite system that transmits and uploads stream-stage and water-quality measurements directly to USGS databases to give virtually "real-time" readings of stream stage, streamflow (computed using the stream stage/streamflow relation), and water-quality measurements.

Water-quality monitoring instrumentation

Like other streams in urban settings, Peachtree Creek is affected by the pressures of urban development, and thus, the potential for water-quality problems are high. Possible sources of problems are:

Picture showins the water-quality monitoring station. It is important to monitor water quality not only to establish baseline water-quality information about Peachtree Creek, but also to allow for timely notification when water quality changes. USGS recently installed an automated water-quality monitoring site at Peachtree Creek. In the picture, the white tube on the right contains probes and instruments submerged in the stream. The structure on the left houses the data-transmission and automated stream-sampling and storage equipment.

Picture showing the tube that contains probes that continually measure temperature, specific conductance, dissolved oxygen and pHThe tube shown in this picture contains probes that continually measure temperature, specific conductance, dissolved oxygen and pH. It also contains tubes to collect water samples during storm events and store the samples in the refrigerated housing structure. It is important to sample the water during storm events, because it is during high water that some water-quality problems, such as high levels of bacteria, sediment, and nutrients (nitrogen and phosphorus) occur.

Sources and more information

 • Discharge measurements at gaging stations, USGS Techniques manual
 • A Day in the Life of a USGS Water Scientist
 • Effects of Urban Development on Floods
 • How Does the USGS Collect Streamflow Data?

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