Risk Analysis on Cascade Breaching of the Tangjiashan Landslide Dam and Two Smaller Downstream Landslide Dams

The 2008 Mw 7.9 Wenchuan earthquake triggered at least 257 landslide dams, most of which formed in series along rivers. The failure of an upstream dam could cause the failure of dams downstream one after another. The cascade dam breaching may result in sharp increase of flood and more serious damage downstream. This paper aims to analyze the risks on cascade breaching of the Tangjiashan landslide dam and two smaller downstream landslide dams, which were triggered by the Wenchuan earthquake. The paper first simulates the cascade breaching of these three landslide dams. A modified DABA model is applied for this purpose, in which the water-soil interactions are simulated with erosion and shallow water flow theory. A human risk analysis model, named HURAM, is applied to analyze the cascade breach risks of these three dams. Two scenarios, namely, the simulated real case and the case with the highest flood with overlapping effect, will be considered to show the characteristics of the cascade dam breaching risks. It is found that cascading dam breaching is very likely to form multiple-peak floods which may cause multi-round impact to the people downstream. The overlapping effect of cascading dam breaching would amplify the breach flood risk to the people downstream.