CHAPTER 6 - MEASURING AND RECORDING WATER STAGE OR HEAD
2. Datum of Gage
A convenient and meaningful elevation datum should be selected for the station. The operating datum for the station should be set below the water-stage elevation for zero flow. The operating datum can be referenced to mean sea level. The datum should be permanent for the expected life of the station and should be referenced to at least two or three other benchmarks that are independent of the gaging structure.