气候变化影响下藏东南帕隆藏布流域高山区泥石流的地貌效应

高海拔或高纬度山区（尤其高山冰川及冻土急剧消退区）常孕育适宜泥石流发育的地形和物源条件。气候变化（如升温、强降雨事件增多等）影响下,高山区潜在孕灾环境更易于成灾,泥石流成为主要的灾害类型和物质输移方式,也是高山区地貌变化的重要驱动力。由于野外监测困难,数据资料匮乏,鲜有针对高山区泥石流过程地貌效应的分析报道。以中国藏东南高山区泥石流多发的帕隆藏布流域为研究区,以古乡沟、天摩沟和扎木弄沟为典型小流域,结合遥感影像、DEM数据、无人机航拍、高精度RTK测量和野外踏勘调查,分析泥石流沟道地貌发育特征（冲淤变化、平面摆动）及其对主河河流地貌的影响,并探讨大规模泥石流事件影响下河谷地貌的长期演变趋势。高山区泥石流过程强烈塑造沟道自身地貌,上游物源区深切展宽和溯源蚀退,沟口堆积扇冲淤变化受控于泥石流事件规模和水流强度。泥石流过程显著影响主河道河流地貌,造成主河道横向冲淤和摆动,并影响堰塞体上游河段平面形态发育。长时间尺度上,河谷地貌在平面上发育形成宽窄相间的藕节状而在纵剖面上形成台阶状形态。

Geomorphic effects of debris flows in high mountain areas of the Parlung Zangbo basin,southeast Tibet under the influence of climate change

High altitude or high latitude mountain areas, especially alpine glaciers and rapidly shrinking permafrost regions, provide suitable topography and material source for the development of debris flow. Under the influence of climate change, such as rising temperature and increasing heavy rainfall events, the potential hazard inducing environment of alpine regions is more likely to trigger hazards. As an important natural hazard and mass flow type, debris flow has become an important driving force of geomorphologic evolution in alpine regions. However, few research reported debris flow processes and its geomorphologic effects in alpine regions due to the difficulty of field monitoring and lack of data. We first analyzed the morphologic effects of alpine debris flow based on a case study on the Parlung Zangbo basin (with three typical debris flow prone gullies, i.e., Zhamunong, Guxiang and Tianmo), located in southeast Tibet, where debris flow occurs frequently. Combined with remote sensing image, DEM data, UAV aerial photography, high-accuracy survey of RTK and field recording, the geomorphic development characteristics of debris flow gully (such as erosion-deposition variation and wandering) and its influence on river morphology of main channels were analyzed. The long-term evolution of river valley morphology under the influence of large-scale debris flow events was also discussed. The debris flow processes in alpine regions strongly shaped gully morphology. The upstream gully channel is eroded and expanded strongly, and the erosion-deposition variation of debris flow deposited fan is determined by the scale of debris flow events and flow intensity. Debris flows significantly affect the river morphology of a main channel, which lead to lateral scouring/silting and wandering of the main channel, and affect the planform channel pattern development of upstream of the landslide dam. In the long term, the river valley morphology would evolve into a wide and narrow alternating planform and a stair-case like longitudinal profile.