This International Standard specifies methods for determining stage-fall-discharge relationships for a stream reach where variable backwater occurs either intermittently or continuously. Two gauging stations, a base reference gauge and an auxiliary gauge are required for gauge height measurements. A number of discharge measurements are required in order to calibrate the rating to the accuracy required by this International Standard. The preparation of rating curves is not described in detail in this International Standard. NOTE For a more detailed description of preparing rating curves, see the methods described in ISO 1100-2