Vol16 No.11: 2502-2518
【Title】Effects of river flow velocity on the formation of landslide dams
【Author】CHENKun-Ting1; CHENXiao-Qing1,3,4; HUGui-Sheng1; KUOYu-Shu2*; CHENHua-Yong1,3,4
【Addresses】1 Key Laboratory of Mountain Hazards and Earth Surface Processes, Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu 610041, China; 2 Department of Hydraulic and Ocean Engineering, National Cheng Kung University, Tainan 70101, Chinese Taipei; 3 CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China; 4 University of Chinese Academy Sciences, Beijing 100049, China
【Corresponding author】KUO Yu-Shu
【Citation】Chen KT, Chen XQ, Hu GS, et al. (2019) Effects of river flow velocity on the formation of landslide dams. Journal of Mountain Science 16(11). https://doi.org/10.1007/s11629-018-5319-1
【Abstract】Natural dams are formed when landslides are triggered by heavy rainfall during extreme weather events in the mountainous areas of Taiwan. During landslide debris movement, two processes occur simultaneously: the movement of landslide debris from a slope onto the riverbed and the erosion of the debris under the action of high-velocity river flow. When the rate of landslide deposition in a river channel is higher than the rate of landslide debris erosion by the river flow, the landslide forms a natural dam by blocking the river channel. In this study, the effects of the rates of river flow erosion and landslide deposition (termed the erosive capacity and depositional capacity, respectively) on the formation of natural dams are quantified using a physics-based approach and are tested using a scaled physical model.We define a dimensionless velocity index vde as the ratio between the depositional capacity of landslide debris (vd) and the erosive capacity of water flow (ve). The experimental test results show that a landslide dam forms when landslide debris moves at high velocity into a river channel where the river-flow velocity is low, that is, the dimensionless velocity index vde > 54. Landslide debris will not have sufficient depositional capacity to block stream flow when the dimensionless velocity index vde < 47. The depositional capacity of a landslide can be determined from the slope angle and the friction of the sliding surface, while the erosive capacity of a dam can be determined using river flow velocity and rainfall conditions. The methodology described in this paper was applied to seven landslide dams that formed in Taiwan on 8 August 2009 during Typhoon Morakot, the Tangjiashan landslide dam case, and the Yingxiu-Wolong highway K24 landslide case. The dimensionless velocity index presented in this paper can be used before a rainstorm event occurs to determine if the formation of a landslide dam is possible.
【Keywords】Natural dam; Landslide; Depositional capacity of landslide debris; Erosive capacity of water flows