CHAPTER 6 - MEASURING AND RECORDING WATER STAGE OR HEAD
The stage of a stream, canal, or lake is the height of the water surface above an established datum (Buchanan and Somers, 1965). The head in a water measurement structure or device can be defined similarly. The stage, or gage height, of the water is usually expressed in feet and hundredths of a foot. Records of stage are important in stream gaging because the rate of flow is plotted against stage in preparing discharge curves. After a curve has been established for a stable channel, rate of flow can be directly determined from stage reading. Reliability of the stage reading is, therefore, of great importance. Head measurements in all types of water measurement structures, including various flumes, weirs, and gates, are equally important. Records of gage height may be obtained from a series of systematic readings on nonrecording gages or from automatic water-stage recorders. Laser, satellite, microwave, and electronic systems can be used to transmit gage readings from either nonrecording or recording gages.