EFFECTS OF BED ERODIBILITY ON NON-COHESIVE FLUVIAL DIKE BREACHING INDUCED BY OVERTOPPING FLOWS

Failure of fluvial dikes induced by overtopping flows can lead to devastating floods, causing significant loss of lives and damages to infrastructure and environment. Accurate prediction of the breach opening, and breach discharge is crucial to achieve a sound assessment of the inundation risk and to design appropriate countermeasures. The complexity of the breaching problem is attributed to the large number of factors influencing the physical processes at work to grow the breach. The present work is part of an ongoing experimental research program on the breaching of non-cohesive fluvial dikes due to flow overtopping. The effect of bed erosion in the main channel, floodplain and dike foundation on the breach expansion and discharge was investigated. The laboratory configuration required the filling of the main channel and floodplain with a 0.1 m layer of sand (1 mm in diameter) over which the 0.3 m high dike composed of the same material was placed. Laboratory observations included time series of water levels in the main channel, time series of flow discharges in the main channel and across the breach, surface velocity using the Large Scale Particle Image Velocimetry (LSPIV) method, and the evolving 3D dike geometry using a non-intrusive Profilometry laser technique. Each laboratory test was compared to equivalent rigid main channel and floodplain beds. Results showed that the three-staged breach dynamics were relatively the same in erodible and rigid bottom cases. However, the bottom erodibility generated the formation of deeper breaches, increasing the breach outflow, particularly during Stage 1 (breach formation). During Stage 2 (breach development), a more incised breach channel formed, with weaker erosion at the breach downstream toe, thus promoting the breach stabilization.