The 24th IAHR-APD Congress (24th IAHR-APD Congress)

117 / 2024-02-07 19:58:04

Co-evolution processes and interaction of braided channels, sand bars and riparian vegetation in the middle Yarlung Tsangpo River

braided river,sand bar,riparian vegetation,channel morphology,Yarlung Tsangpor River

In recent decades, the expansion of natural or artificial vegetation in the middle reaches of the Yarlung Tsangpo River (YTR) in the Tibetan Plateau has largely impacted the morphology and stability of large braided channels. Nonetheless, comprehensive studies in these braided channels have been hindered by the harsh environment and challenges in data deficiency. This study focuses on three main braided reaches in the middle YRT (i.e., Rikaze, Qushui-Naidong, and Yarlung Tsangpo-Niyang confluence). Applying MNDWI and NDVI derived from remote sensing data, we analyzed spatiotemporal changes in braided morphology and vegetation distribution. Our study reconstructed the co-evolution processes of braided channels, sand bars, and riparian vegetation from 1988 to 2023. Additionally, through field measurement in 2018-2023, we elucidated the pattern and mechanism of riparian vegetation impacting on morphological changes and stability across various spatial scales in braided channels. These findings are summarized here: (i) Riparian vegetation within braided channels of the middle YTR has shown a consistent increase, predominantly concentrated and effectively influencing the bars close to both river banks; (ii) Channel morphology on the transects with well-distributed vegetation shows minimal interannual variations, and is less affected by flood flows in comparison with that on transects with poor or no vegetation, indicating the crucial role of vegetation growth and encroachment in stabilizing braided river morphology; (iii) Vegetation density is a vital factor in exerting an effective influence on sustaining braided channel morphology, i.e., vegetation on sand bars with varying degrees of sedimentation exhibiting different capabilities in sediment interception, including three patterns such as tree trunks, branches, or canopy layers in the vertical direction; (iv) Overall, vegetation distribution in the middle YTR remains insufficient, and braided channel morphology is primarily adjusted due to disturbances from flood flow and sediment. Therefore, it’s essential to enhance implementation of water conservation and ecological engineering measures to control sediment transport and riverbed erosion in braided channels.