Dam breach modelling: influence on downstream water levels and a proposal of a physically based module for flood propagation software

The influence exerted by the method used for computing the dam breach hydrograph on the simulated maximum water levels throughout the downstream valley is essential for selecting a specific computing module to be implemented in the numerical codes used by practitioners. This module should be able to balance the need for a reasonable physical description of the phenomenon and, at the same time, limit as much as possible the maximum number of parameters. In order to feed a debate on this field, in this paper the performances of some parametric models used for the dam breach module implemented in the popular HEC-RAS software, and a simplified but physically based model have been analysed. The performances of the dam breach models have been assessed with reference to the historical event of the Big Bay dam, using both one-dimensional and two-dimensional (1-D and 2-D) flood propagation modelling. The results show that the physically based model considered here, without any operations of ad hoc calibration, has provided the best results in predicting computation of that event. Therefore, it may be proposed as a valid alternative to parametric models, which need the estimation of some parameters that can add further uncertainties in studies like these.