CHAPTER 6 - MEASURING AND RECORDING WATER STAGE OR HEAD
8. Setting the Datum
Setting the zero or datum elevation is one of the most important tasks when setting up a gaging station in a stream, river, or on a measurement structure. Care must be taken to ensure that the datum is below the zero flow level and that it can be independently located from points outside of the gaging structure. Datums are typically set using surveying techniques, often relating the datum elevation to mean sea level. A staff gage is usually located nearby to verify that the gaging station is operating correctly. Periodic checks on the datum elevation should be performed to ensure that no movement or settling of the stilling well or structure has occurred. Erroneous readings from a gaging station are many times directly related to the setting or shifting of the datum.