Dam break flow modelling with uncertainty analysis

Handling uncertainties in dam break flow modelling is of primary interest. Therefore, a procedure is presented here to conduct systematic analysis of the uncertainties resulting from the roughness coefficient, the breaching hydrograph and topographic data. The flow simulations have been conducted with the model WOLF 2D developed at the University of Liege. This two-dimensional flow model is computationally too costly to perform a high number of repeated runs, as needed for Monte Carlo simulations. Therefore, a “reduced complexity model” has been set up, in the form of multidimensional Hermite polynomials. This method, developed by Isukapalli et al. (2004) and first applied to dam break flow by Niemeyer (2007), involves a reduced number of runs of the complete model to calibrate the polynomials. This paper shows the applicability and efficiency of the methodology, but it also discusses previously unreported shortcomings of the approach, together with hints to overcome them. Results of such uncertainty analysis for dam break flow modelling disclose crucial information for practical risk management. In particular, they reveal that the uncertainty ranges on maximum water depth and time of arrival of the front are not symmetric (overestimation vs. underestimation) and very unevenly distributed in space.