The U.S. Geological Survey (USGS) has thousands of these stream-gaging systems installed nationwide. It is still the most common way to measure the
heights (and, indirectly,
the amount of water flowing at any given time)
of streams. The technology is changing. The more modern systems
detect the heights of streams and transmit that
information via satellites to a USGS office.
In the past, the most common type of stream gage worked by recording stream height on a moving paper roll. Nowadays gage heights are stored electronically in an instrument in the box on top of the big pipe (stilling well).
Here's how some of these gages generally work: The big
metal pipe going down into the water is a stilling well.
The box on top (made of metal to resist bullets!) contains a
measuring instrument (data logger) that
has a pulley with a metal wire holding a float
at one end. As the water in the stream moves up and down, the water in
the vertical metal pipe moves also. The float on the wire goes up and
down with the water. As the wire moves, the pulley turns, which
changes the gage-height reading. Then the gage-height readings
are recorded automatically in the data logger.
When a technician visits the site they
can either take data-storage card back to the office, or
download the data on site.
The most modern gage houses have a satellite-transmission system that can upload data right to the USGS office -- essentially a real-time system.
• Discharge measurements at gaging stations, USGS Techniques manual
• A Day in the Life of a USGS Water Scientist
• Willie Takes a Field Trip, a coloring book that introduces tomorrow's scientists to water