Evolution of braided channels at the confluence of Yarlung Tsangpo and Niyang River from 1986—2021

The morphology and variation of braided channel at the confluence reach of Yarlung Tsangpo River (YTR) and Niyang River are affected by the inflow of Niyang River, valley boundary and vegetation conditions.The spatio-temporal variation and complexity of of the braided river are of importance to further study.The remote sensing images from 1986 to 2021 were used to extract the morphological features of braided channels, sandbar and vegetation (channel migration rate, sinuosity, area, et al).We further analyze the morphological characteristics and evolution processes of complex braided channels.The results show that maximum migration rate of the main channel is 483 m/a, the sinuosity reduces by 3.43%, and the vegetation cover area increases up to 8.05 km².Owing to the difference of boundary conditions and hydrological conditions, the main channel of the Milin-Paizhen reach oscillates laterally before the Niyang River flows into the YRT, and migrates laterally and longitudinally after Niyang River flows into the channel.Since 2013, 11.8% of the vegetation coverage in the river channel has a positive feedback of erosion inhibition and deposition promotion, and enhanced the stability of the sandbars.