Characteristics, mechanisms and prevention modes of debris flows in an arid seismically active region along the Sichuan–Tibet railway route, China: a case study of the Basu–Ranwu section, southeastern Tibet

The Basu–Ranwu section of the Sichuan–Tibet railway is in an arid and tectonically active valley characterized by rugged topography, sharp river incision and severe debris flow events. The study aims to provide scientific support for the prevention and control of debris flow in this section by revealing the dynamic characteristics, main controlling factors and distribution rules of debris flow. Research based on the analysis of field investigation data, remote sensing images, DEM and geological map has yielded the following results: (1) the forty-eight debris flows in the study area can be divided into five types based on the formation conditions, which are zonally distributed along the fault zone and also varied vertically in space and depended on the hardness of the underlying strata. (2) A complex geological and environmental background has provided appropriate material sources and favourable potential energy conditions conducive to the formation of disastrous debris flows. Additionally, the development of debris flows was affected by antecedent earthquakes and droughts, and disastrous debris flows are triggered by an abundant source of water. (3) The study area is located in the arid area, where the rainfall runoff is small and the scale of debris flow is relatively small, except for a few glacial lake outburst debris flows; therefore, the debris flow in this section can be controlled; prevention modes of debris flow hazards have been proposed for the railway engineering based on the types of railway engineering and the scale and type of the debris flows. The results provide an important and object scientific basis for route selection for geological engineering projects and for the control of debris flows in the Basu–Ranwu section of the Sichuan–Tibet railway.