Risk assessment for landslide-induced impulse waves in the Three Gorges Reservoir, China

The Three Gorges Reservoir, which is located in an area with a high incidence of geological hazards, has recently suffered great losses owing to landslide-induced impulse waves. Along with the rapid development of cities in the vicinity of the Yangtze River, the Three Gorges Reservoir, with current daily traffic of about 235 large vessels, is an increasingly important logistics channel. The risk related to impulse waves in this channel cannot be ignored. In this study, a combined quantitative-qualitative technical framework is proposed to assess the risk of landslide-induced impulse waves in the Three Gorges Reservoir based on a combination of risk assessment methods for landslides and tsunamis. The proposed assessment method is applied to the Wu Gorge section of the reservoir, which is prone to landslides and consequent impulse waves. A risk analysis is performed on landslides known-to-date to be of potential threat to the Wu Gorge through tsunami genesis, including the Maocaopo landslide, Gongjiafang IV landslide, Ganjingzi landslide, Jianchuandong rockfall, Quchitan rockfall, and Banbiyan rockfall. As communities along the Yangtze River are more likely to be exposed to impulse waves when there is a high water level of 175m above sea level, there are significant differences for areas affected by impulse waves under different water level conditions. The vulnerability of both sailing and moored ships is analyzed by a simple quantitative method, while a vulnerability assessment for riverside communities is performed qualitatively. Based on the results of the risk assessment, the potential landslides can be ranked from high to low level of risk as Jianchuandong rockfall, Banbiyan rockfall, Quchitan rockfall, Gongjiafang IV landslide, Maocaopo landslide, and Ganjingzi landslide. The impulse waves caused by the Jianchuandong rockfall could cause the highest level of human loss, as the Qingshi community will be attacked by it, while the Ganjingzi landslide could cause the highest economic loss (about 8 million RMB or 1.16 million USD), as many wharf boats and vessels docked in the wharf of Wushan County will be attacked by it. The Qingshi and Peishi communities have fallen into the very high-risk rank. The proposed method for risk analysis may provide a basis for the risk priority control of geological hazards and early warning in the Wu Gorge section. However, there is still a long journey before a mature technical framework for risk assessment on landslide-induced impulse waves in reservoirs can be achieved. The methods presented here can help to control, prevent, and reduce the destructive consequences of landslide-induced waves in reservoirs around the world.