Abstract: Geological disasters occur frequently in the Yarlung Tsangpo Grand Canyon, particularly in Yigong Tsangpo River and Parlung Tsangpo River where landslides, avalanches, and debris flows easily block the rivers and give rise to barrier lakes. According to multi-annual Landsat imagery of Yigong Lake, Guxiang Lake, Ranwu Lake, and Tianmo Gully as well as the longitudinal profile fitted by simple function, we analyze the morphological processes of upstream riverbed and its geomorphological significance in association with field investigation in 2011-2017. Taking Yigong Lake as an example, when water depth of the lake increases from 4 m to 8 m, we roughly estimate that the bedload transport rate per channel width increases by about 3 times, which however decays rapidly along the course. Thus, sediment deposition within the lake would be unavoidable. Meanwhile, unstable bars in flood period are eroded and split into irregular bars, which leads to the continuous change of bed morphology in the lake.The research findings provide a new understanding on the response of river morphology to barrier dams.

Key words: barrier dam, landslide, debris flow, riverbed fluvial processes, river morphology, forming sedimentation, river morphology, forming sedimentation, Yarlung Tsangpo Grand Canyon