Risk Analysis of Tangjiashan Landslide Dam

Tangjiashan Landslide Dam, with a height of 82-124 m, a volume of 20.4 million m³ and a reservoir volume of 316 million m³, is the largest landslide dam induced by the Ms 8.0 Wenchuan Earthquake on 12 May 2008. The breaching of the dam threatens more than 1.3 million people downstream. This paper outlines a procedure to estimate the loss of lives (LOL) due to various potential modes of failure of the landslide dam. A regression model with parameters of population at risk (PAR), warning time (WT) is studied. Based on empirical breach parameters, analysis of flood routing in the river downstream the dam is performed using a river analysis program, HEC-RAS. Both the real failure scenario and two assumed overtopping failure scenarios are considered. The inundation area and warning time for each affected zone in each scenario are obtained. A physical model is selected to obtain the population at risk based on historical data and the information of water depth, flow velocity, warning time etc from the analyses using HEC-RAS. Some possible situations of warning time are compared. Based on the regression model with data of PAR, WT, force, and population distribution along the downstream of Tangjiashan Landslide Dam, the LOL can be estimated in different scenarios.