Tracking mass-wasting sediments in the large BrahmaputraRiver system

The impact of mass-wasting events on river systems is typically studied in the immedi-ate aftermath and within close proximity to the source area. However, basin-widehydro-geomorphic responses in large river systems, beyond the immediate post-disaster context, remain poorly understood. In this study, we examine the EasternHimalayan Syntaxis in the Brahmaputra basin, where the Sendongpu glacier valley hasundergone rapid erosion due to major mass-wasting events in 2017, 2018 and 2021.A nearby large-scale event also occurred in 2000 along the Yigong River. We assessthe river’s response to these events using satellite-derived water turbidity indices,water surface elevation, sandbar area and flood extent, at the finest temporal and spa-tial resolution available through Google Earth Engine’s database. Our time series anal-ysis reveals that, following the 2017 event, fine suspended sediment signals can betraced more than 1000 km downstream to the delta, while coarser sediments primar-ily affect river morphology within approximately 100 km of the mountain front. In thiszone, we observed a notable increase in sandbar area and water surface elevation,indicating extensive deposition and channel infilling. Comparison with the 2000Yigong outburst highlights the differing geomorphic effects of rapid, high-magnitudeevents versus slower, more sustained sediment inputs. These findings highlight theneed to integrate mass-wasting-driven sediment processes into flood risk assessmentsand hydropower planning in Himalayan river systems, particularly as such landscapesare increasingly subject to both natural and anthropogenic pressures.