Engineering risk mitigation measures for the landslide dams induced by the 2008 Wenchuan earthquake

More than 257 sizable landslide dams were induced by the 2008 Wenchuan earthquake, which required timely risk mitigation measures. This paper aims to summarize the engineering measures taken to mitigate the landslide-dam risks; provide a method for optimal design of spillways to minimize the risks; and quantitatively evaluate practical options for spillway design with a physically-based dam breach model. The engineering measures taken to mitigate the risks of 37 highly hazardous landslide dams induced by the Wenchuan earthquake are summarized. An optimization method is proposed and applied to the spillway design for the Tangjiashan landslide dam, which is the largest one caused by the Wenchuan earthquake. It is found that the peak outflow rate could be reduced from the recorded 6500 m3/s to 2900 m3/s using the optimal design. A spillway with a shallow and broad cross section is suitable for low-erodibility dams, while a spillway with a deep and narrow cross section is suitable for high-erodibility dams. A spillway with a large longitudinal gradient is beneficial for high-erodibility dams with large dam widths and gentle downstream dam slopes. A spillway close to one bank can reduce the peak outflow rate if the bank is erosion resistant.