Simple Method for Relating Local Stage and Remote Discharge

A simple method is proposed for reconstructing the discharge hydrograph at a river section where only water level is monitored and discharge is recorded at another upstream section. The method, which is based on the assumption that lateral inflows are negligible, has two parameters linked to remotely observed discharge and permits, without using a flood routing procedure and without need of a rating curve at a local site, relating the local river stage with the hydraulic condition at a remote upstream section. Calibration and validation of the method were carried out by comparing its results with those of a hydrodynamic model called MIKE11. The method was applied to simulate five flood events that have occurred along an instrumented reach of the Tiber River in central Italy. The shape characteristics of the reconstructed hydrographs at a gauged section where only local stage was available were similar to those of the hydrographs computed by MIKE11. A comparison between the Muskingum model and proposed method showed also that the latter is more reliable if a hypothetical rating curve must be given at the downstream section.