Overtopping-induced levee breaches considering heterogeneous levee materials and outside flow

In this study, overtopping-induced levee breach experiments were conducted to explore the effect of differences in levee structure on levee breach characteristics, considering the heterogeneity of the levee material and the flow outside the levee. A homogeneous levee composed of silica sand No. 7 and a heterogeneous levee composed of silica sand No. 5 and No. 7 overlapped by two levees were subjected to overtopping-induced levee breaches in the presence of flow outside the dike. Comparison of these processes revealed that the downstream progress of erosion is more plausible than the upstream side due to flow outside the levee. The shape of the breach opening was different during the levee breach process between the levee made of a heterogeneous structure and that made of a single material. Moreover, the rate of widening of the breach opening on the back slope increased at an earlier stage in the former case than in the latter, resulting in a larger overflow rate. To the best of our knowledge, few studies have simultaneously considered the heterogeneous structure of an actual levee and the flow outside the levee.