Landslide dam breaching and outburst floods: A numerical model and its application

Abstract

The damages caused by the breach of landslide dams can be mitigated by making an emergency plan based on the fast and accurate forecast of the resultant outburst floods. This study proposed an advanced physically-based breach model, which can effectively predict the breach evolution and the outflow hydrograph. Variations of soil erodibility along the dam depth are specially considered in this model. To avoid infinite occurrence of soil erosion, an arctangent erosion model is proposed to calculate the erosion rate, two advantages of which against the existing erosion models are demonstrated: better representation of the erosion process and simplified requirement of only one input parameter. The rate of the breach lateral enlargement is considered to vary along the depth, and the breach shape is regarded as a rectangle. The breach model is applied in two case studies of the Tangjiashan landslide dam and the Baige landslide dam. The predictions of breaching geometric parameters and the outflow hydrographic parameters agree well with the field observations. Comparing with the two widely-used landslide dam-break models, the proposed numerical method predicts changes of the lake level and the breach bottom more accurately. Results also prove the importance and necessity of considering soil erodibility along the dam depth. Moreover, sensitivity analysis is also conducted. It can be found that the parameter related to the arctangent erosion model significantly affects the breach evolution and the associated outflow hydrograph, while the influences of the broad-crested weir flow formula and the lateral enlargement rate is not that obvious. The numerical results are not sensitive to the velocity step adopted in the numerical scheme, facilitating the application of the model in the rapid risk assessment for landslide dams.