Physical model test of the influence of the spillway geometry on the scouring and breaching process of landslide-dammed lakes

Unexpected breaching of landslide dams can produce tremendous floods and debris flows, thus greatly threatening the security and property of people living downstream. Research has revealed that erosion via outflow and spillway evolution are the two main causes of landslide dam breaching. Additionally, the excavation of artificial spillways has currently been recognized as an effective risk mitigation measure. In this study, by simulating the breaching process in a flume, it was elucidated that breaching conforms to a water-soil coupling mechanism. Maintaining an unchanged cross-sectional area of the notch, five notches were set on the left side of the dam to explore the influence of notch geometric dimensions on the breaching process. This study suggests that the breaching process could be chronologically divided into four stages: (1) seepage failure, during which the skeleton of the dam is damaged by seepage; (2) slow erosion, in which water begins to overflow under a low discharge; (3) drastic failure, during which drastic collapse of the dam crest causes a sudden increase in discharge; and (4) equilibrium state, in which the residual dam remains stable. This study further indicated that the notch height-to-width ratio plays a vital role in the process. An increase in height-to-width ratio could ensure more continuous lateral expansion, while vertical evolution could be inhibited. Finally, the discharge data indicated that to minimize the discharge and mitigate the hazards due to breaching, it is important to control the notch geometry.