Experiments on the characteristics of breach variations due to natural dam overtopping

Natural dams are a common geological disaster that can threaten the safety of people and buildings for several hundreds of kilometres downstream. However, the failure characteristics of natural dams are still unclear, especially the variation characteristics of breaches. In this paper, 20 groups of flume experiments are conducted. Based on the experimental results, the longitudinal and lateral variations of breaches during overtopping are studied. In addition, the relationship between the width and depth of breaches is quantitatively analysed. The results are as follows: during the process of a natural dam overtopping failure, the relationship between the breach depth and time is controlled by the slope of the flume. It is demonstrated that there is an “S” shape when the slope is small and a straight line when the slope is large. In terms of the rate of lateral expansion of the breach, it is demonstrated that the rate of lateral expansion of the breach is smaller in the earlier stage and later stage and is larger in the middle stage. The relationship between width and time is S-shaped. The slope at the bottom of the breach fluctuates during the entire process. The main reason is that the dam break is accompanied by backward erosion, but the slope remains below the underwater angle of repose of the material. Based on the experimental data, the quantitative relationship between the width and depth of breach is investigated. On the basis of the quantitative relationships, a mathematical model of dam breaks is established. The rationality of the model is verified by comparison with actual cases, and the relationship between the width and depth of breaches is proved to be reasonable.