Streamgages are structures that house equipment that measures and records stream stage and other parameters before transmitting that data to centralized computers via satellites.
Sites for streamgages are ideally chosen where the stream is reasonably stable, and the flow of the water is controlled by the physical structure of the stream without interference in the stage from reservoirs or tributaries.
The physical structure of a streamgages has changed through time. Although they may look different on the outside, all streamgages serve the same purpose: safely housing specialized equipment that collects and transmits data.
At most streamgages, stream stage is measured using an orifice line (see figure below) secured in a pool. The sturdy hose has pressurized air or nitrogen gas pushed through it and determines the stage (height) of the stream based on the amount of back pressure in the hose.
The stream stage recorded by the equipment in the streamgage is verified at every visit by comparing the recorded stage to the staff plate (shown at right). The elevation of the staff plate is surveyed frequently to ensure it hasn't moved due to high flows or other events.
Get the whole picture: From Gage to Page: A Look Into How USGS Helps You Know the Flow
The steps involved in getting the data to your fingertips, generally include: