Numerical and experimental modelling of overtopping induced river dikes failure

Abstract

Worldwide, the failure of river dikes causes a large number of casualties and flood damage. Different failure modes can induce the collapse of these structures; but overtopping is by far the most frequent one. Although many studies were conducted to better understand the breaching process, most of them focused on dam configurations (i.e. flow normal to the structure) or on coastal dikes. In this research, we aim to improve the current understanding of the breaching of river dikes (i.e. flow parallel to the structure), which differs significantly from the frontal configuration. The objective is to contribute to the development of a numerical tool able to predict the evolution of a breach and the induced flow in river dikes undergoing overtopping. The present research is structured along two main lines. On the one hand, an experimental model was built in the laboratory of Engineering Hydraulics at the University of Liege in order to collect experimental data which give a better insight into the physical processes involved in the dike breaching. Specifically, the experimental observations highlight the influence of the upstream flow conditions (in the main channel) on the shape of the breach and on its dynamic evolution (deepening vs. widening). On the other hand, three numerical models of increasing complexity were studied and compared with existing data. The three models include a hydraulic module and a breaching module; but they differ in the representation of the flow (simple assumption such as constant head vs. fully dynamic flow model). After successfully validating the upgrades that we coded in these models, we performed numerical simulations of our experimental tests. The results demonstrate that the model is operational and provides some indications on dike breaching process. However, the module computing the breach geometry evolution is still at an early stage and needs further refinements based on more experimental tests.