Overtopping induced fluvial dike breaching: lessons from experimental and numerical studies

Overtopping of fluvial dikes (i.e. levees) can promote breach formation and potentially brutal dike failure, leading to the inundation of the protected area. Flood risk management and prevention require a precise quantification of the hazard. Accurate estimate of the flow through the breach is paramount, for which a precise understanding of the breach formation and expansion is required. An experimental program was conducted to fill this gap by investigating the physical processes involved in overtopping induced fluvial dike gradual breaching. Experiments were conducted on two distinct experimental setups, each consisting of a main channel and floodplain area separated by an erodible fluvial dike. The focus was made to study overtopping induced spatial erosion of homogenous, non-cohesive dikes. Measurements included continuous scanning of the 3D dike geometry using a non-intrusive method (Laser Profilometry Technique), which was designed and developed specifically for the present works. Tests conducted under controlled flow and dike configurations allowed assessing the effects of channel inflow discharge and floodplain confinement on the breach development and outflow. Effects of dike material size, apparent cohesion, and bottom erodibility were studied as well. In the present paper, the most important findings are presented. Additionally, the flow and dike breaching were simulated using the two-dimensional depth-averaged code TELEMAC-2D. This allowed assessing the performance of a detailed morphodynamic code for dike breaching processes.