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The statistical characterization of extreme floods largely benefits from the reconstruction of historical floods, making use of various documentary sources and of hydrodynamic models. The two-dimensional (2D) modelling approach provides a higher accuracy and detail with respect to one-dimensional (1D) modelling. On the other hand, 2D models require a large amount of topographic and hydraulic information for calibration, having several parameters to be determined, which makes the calibration prone to underdetermination. To address this issue, we provide here practical guidance for the effective calibration of 2D models for the reconstruction of historical floods in urban areas with a limited amount of information available. Specifically, we show how to constrain model parameters by distinguishing among "static," "dynamic" and "global" data and their role in the calibration procedure. The latter is exemplified by a relevant application to the reconstruction of the great 1870 flood of Rome, Italy. [ABSTRACT FROM AUTHOR]

The article focuses on the simulation of the great flood of December 1870 in Rome. A depth-integrated two-dimensional varied flow model simulates Tiber River flood of December 1870. The development of the model is an important step in a research program aimed at the reconstruction of the stage discharge relationship of the Ripetta gauge in the nineteenth century. The use of the model allows some further insight into the behavior of the flood in the flooded areas of the town. The model represents fairly well the actual surface elevation of the flood, and is therefore a useful instrument for evaluating the stage discharge relationship of the Tiber at Ripetta during the nineteenth century.