USGS Streamgage Diagram

Detailed Description
USGS streamgage diagram
Most U.S. Geological Survey (USGS) streamgages measure stage and consist of a structure in which instruments used to measure, store, and transmit the stream-stage information are housed. Stage, sometimes called gage height, can be measured using a variety of methods. One common approach is with a stilling well in the river bank or attached to a bridge pier, as this diagram shows.
Here are some links for you to learn more about how the USGS measures river stage and how, using stage, stream discharge (streamflow) is computed:
Sources/Usage
Public Domain.