Longitudinal profile analysis and spatial distribution characteristics of tributaries in the knickzone of the Lancang River

The Lancang River, as the upper reach of the Mekong River, is the most one important rivers in Asia. There is a over 500 km knickzone  (27.5-30.17°N) of the Lancang River where it descends  the southeastern margin of the Tibetan Plateau. To explore the role of tectonics in controlling river incision at regional and local scales, we analyzed the rive  profile of Yunlong-Chaya tributary and calculate the channel steepness and incision amount within and below the knickzone, and reconstruct the spatial patterns of river. The results show that most of the tributaries are in a transient state with a or two knickpoints. The knickpoint recovery suggest a incision amount of ~ 50-2700 m and northward increasing trend. At the same time, the knickpoint elevation and mean channel steepness index of tributary also show the similar trend of northward increase. The low temperature thermochronology data suggest that the erosion rates and spatial variation of river terrace  are similar to the regional erosion rates on the million-year and tens of million-year scales. The spatiotemporal variation of the erosion rates along the Yunlong-Chaya reaches indicate that tectonics plays a key role in shaping the landscape of the southeast Tibet.