Functional characteristics of a braided river in the Qinghai-Tibet
Plateau, China
Abstract
In this study, we unveiled the lumped effects at the reach spatial scale
over three decades in one of the braided rivers in the Qinghai-Tibet
Plateau of China, the Upper Lancang River (ULR). Using Landsat images
obtained in 13 years between 1989 and 2018, 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, but it seems that this system can be very
sensitive to global change due to vegetation encroachment following
temperature rising and decreases of low flows.