EP015-01
Functional characteristics of a braided river in the Qinghai-Tibet Plateau, China

Tuesday, 8 December 2020: 19:00
Virtual
Peng Gao, Syracuse University, Syracuse, NY, United States, Zhiwei Li, State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan, China, Yuchi You, Changsha University of Science & Technology, Changsha, China, Yinjun Zhou, Changjiang River Scientific Research Institute, Wuhan, DC, China and Hervé Piegay, Centre National de la Recherche Scientifique - CNRS, Lyon, France
Recorded Presentation
Abstract:
Functional characteristics of braided rivers located in the Qinghai-Tibet Plateau, China with very high elevations (> 3400 m) have not been well understood primarily due to their remote locations and harsh physiographic conditions. In this study, we unveiled their lumped effects at the reach spatial scale over three decades in one of these braided rivers, the Upper Lancang River (ULR). Using Landsat images obtained in 13 years between 1989 and 2018 during the dry season (November to early May) when water levels were low and comparable over years, we extracted flowing and non-flowing channels, active channel widths (unvegetated bars and flowing channels), and calculated lateral shifting rates of the main channel for the 13 periods. We also developed an empirical equation between vegetation area (Av) calculated from the high-resolution ortho-photo derived from an Unmanned Aerial Vehicle survey and Normalized Difference Vegetation Index for pixels of the Landsat image obtained at the same time. This relationship allowed us to estimate Av for other 12 selected years. We found that (1) braiding intensity increases with low discharges, indicating that the ULR is a very well-connected braided system with groundwater providing a large set of aquatic habitats, (2) this braided system is very well-supplied and actively shifting in relation to peak flow and flood duration, and (3) The ULR supports a progressive vegetation encroachment, which seems to be linked to temperature rising. Our study showed several similar morphological patterns to those in other braided rivers, such as the ones observed in the European Alps but much more active, well-supplied and highly connected. These similarities suggest that similar morphodynamic processes might take effect in the braided rivers with very high elevations and potentially high spots of biodiversity, indicating the ULR may be a reference for this region similarly to the Tagliamento in the Alps.
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