Accurate prediction of the failure of landslide dams due to overtopping and the pertinent evolution are essential for the estimation of outburst flow hydrographs and resulting inundation risks. Dr. ZHOU Gongdan and his research group from the Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, recently conducted physical model tests with a 45-m-long concrete flume to study the longitudinal evolution of the overtopping failure process of landslide dams under different upstream inflow discharges.  

Results reveal that the longitudinal evolution of the dam failure along the flow direction is a result of bed-load erosion. A new longitudinal evolution model is proposed in this study which features three different stages (Figure 1). Stage 1 is characterized by the movement of the erosion point from the downstream dam crest to the direction of the upstream dam crest and downstream towards the dam toe. In Stages 2 and 3, a spindle -like erosion is observed along the flow direction, indicating that the erosion rate initially increases and then decreases along the outburst flow direction. Furthermore, a linear equation E = k_d (τ-τ_C) can be used to define the relationship between the erosion rate and shear stress during the dam-breaching process (Stage 2 and 3) as illustrated in Figure 2. This relationship is found to be true even for real events such as the Tangjiashan landslide dam failure. This shows that the ‘apparent’ erosion resistance (τ_C) of landslide dams against the incoming flow increases along the flow direction (Figure 2). 

This study is financially supported by the National Natural Science Foundation of China (grant Nos. 41731283, 11672318). This study has been published on the journal of Geomorphology (2019, 334: 29-43). 

Figure 1. Proposed longitudinal breach profile evolution of landslide dams based on modeling tests (Image by ZHOU Gongdan).  

Figure 2. The relationship between erosion rate and shear stress at the different sections for all experiment set-up during Stages 2 and 3 (Image by ZHOU Gongdan).