Modeling flood and breach evolution of the landslide dam due to overtopping

•A simplified physically-based model aimed at simulating overtopping-induced dam breaching is presented.•A breach evolution mode, based on the log-spiral slip surface, is developed to consider breach slope collapse.•The breach evolution mode adheres to the principle that soil erosion occurs solely beneath the water surface.•A number of empirical parameters are investigated for their effect on dam breaching. Dam breaching induced by overtopping is a multifaceted hydraulic and geotechnical phenomenon frequently observed in landslide dams. This study introduces a simplified physically-based numerical model aimed to simulate overtopping-induced dam breaching. The model employs a broad-crested weir formula considering the upstream slope to calculate the outflow discharge. In consideration of breach slope collapses, a breach evolution mode is described based on the log-spiral slip surface. The mode adheres to the principle that soil erosion occurs solely beneath the water surface. The proposed simplified model was applied to simulate the overtopping breaching of Tangjiashan and Baige landslide dams in China. The obtained results exhibit good agreement with available field measurements and numerical solutions. Furthermore, a series of parameter analyses were conducted to investigate the influence of several highly empirical parameters on the dam breaching process. The findings reveal that the peak discharge is predominantly influenced by the limiting soil erosion rate defined in the hyperbolic soil erosion equation, whereas the peak arrival time is mainly affected by the critical flow velocity. In cases where soil grading information is unavailable for estimating the Manning roughness coefficient, a value of 0.035 can be adopted. The critical flow velocity and the limiting soil erosion rate are critical parameters that require careful determination.