Fluvial Dike Breaching Induced by Overtopping: Lessons from Experimental and Numerical Studies

Overtopping of fluvial dikes can lead to its breaching and failure and cause devastating inundations in the areas protected. Flood risk management and prevention require a precise quantification of the hazard. The accurate estimate of the flow across the breach is paramount, requiring a detailed understanding of the breach expansion. Existing approaches are often the result of investigations on overtopping of embankment dams. The application of such approaches to fluvial dikes is not reliable, and processes underpinning the breach expansion are still under research. An experimental program was conducted to fill this gap by investigating the physical processes involved in fluvial gradual dike breaching induced by overtopping. Experiments were conducted in two laboratory setups. The focus pointed at the spatial erosion of homogenous, non-cohesive fluvial dikes. Measurements included the continuous scanning of the dike geometry by a non-intrusive Laser Profilometry Technique. Tests conducted under controlled flow and dike configurations allowed for assessing the effects of the channel inflow discharge, downstream channel regulation system, and floodplain confinement on the breach development and outflow. Effects of main channel size, dike material size, apparent cohesion, and bottom erodibility were studied as well. The present research highlights the most important findings. The flow and dike breaching features were additionally simulated using a two-dimensional morphodynamic numerical code.