River gauges measure water levels and, in some cases, water discharges.
As water rises inside the well, measurements are taken. Some gauges are pressure transducers, which are tubes that pump nitrogen bubbles into a stream. There is a direct relationship between the amount of pressure needed to push the bubble into the stream and the water level. The U.S. Geological Survey shares the data with such agencies as the National Weather Service, which uses it to forecast floods. The nation's flood warning system is being weakened, needlessly placing lives and property at risk, experts at two federal agencies warn.