堰塞体堵江对雅鲁藏布大峡谷地区河流地貌的影响

雅鲁藏布大峡谷地区地质灾害频繁,以易贡藏布与帕隆藏布两条支流为主,这2条河流沿岸发生滑坡、崩塌和泥石流易形成堰塞体堵塞河道并形成堰塞湖。基于易贡湖、古乡湖、然乌湖和天磨沟的多年遥感影像以及函数拟合纵剖面分析与野外调查,分析堰塞体上游河床演变过程及其河流地貌学意义。以易贡湖为例,当堰塞湖水深从4 m增至8 m时,估算其单宽输沙能力增加约3倍,但输沙率沿程快速衰减,泥沙进入堰塞湖中发生严重淤积,从而发育较多成型淤积体,同时洪水期水流将原有成型淤积体(如沙洲)冲刷分割为不规则的群体沙洲,使得湖内河床形态持续变化。本成果为研究河流地貌对堰塞体堵江的响应提供了基础。

Impacts of River-blocking Barrier Dams on Morphological Processesof Upper Alluvial Channel in Yarlung Tsangpo Grand Canyon

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.