Continuous discharge monitoring using non-contact methods for velocity measurements: Uncertainty analysis

At gauged site, water stage and discharge hydrographs can be related also during unsteady flow conditions, using the one-dimensional diffusive hydraulic model, DORA, and exploiting sporadic surface velocity measurements carried out with a radar sensor, during the rising limb of the flood. Indeed, starting from the measured surface velocity, the application of a simplified entropic velocity distribution model allows obtaining the benchmark discharge for the Manning's roughness calibration. The aim of this work is twofold. First, to address the uncertainty of the approach. Second, to detect the minimum water level along the rising limb in which the occasional surface velocity measurement should be carried out. Several historical events recorded along the Upper Tiber River, Central Italy, are used to this end. Results show that when the DORA model calibration is performed at water levels greater than 60 % of maximum historical one, it is possible to estimate the whole discharge hydrograph with good accuracy and quite narrow confidence band.