A conceptual model to quantify probabilistic dike breach outflow.

Hydrodynamic models can provide accurate information on the consequences of a dike breach, but their long computation times hinder the analysis of uncertainties and scenarios during a time-sensitive emergency situation. Conceptual models use simplified rules and relations, and allow for much faster computation while preserving reasonable accuracy. In this study, we develop a conceptual model with breach growth that estimates the dike breach outflow for varying river discharge events and for varying dike breach locations along the Rhine's bifurcations in the Netherlands and Germany. The results show that the model is able to provide a good estimate of the breach outflow, regardless of river discharge waves shape and peak discharge. The model achieves an approximate error of 10 to 15% compared to an operational hydrodynamic model of the study area. Its computation speed allows the analysis of thousands of scenarios per minute, enabling decision makers to probabilistically analyse breach outflow hydrographs at sampled critical water levels for an incoming extreme river discharge wave. We conclude that this conceptual model can provide realistic first estimates of breach outflow for large-scale dike breaches, while requiring little input data and computational time.