This paper is the result of fluvial geomorphology research in the Lancang River region.
Objective The Lancang River, the upper reach of the Mekong River, is one of the major rivers in Asia. It flows through the southeastern margin of the Tibetan Plateau, passing through several Southeast Asian countries before draining into the South China Sea. The river long profile shows a knick−zone over 500 km in length (27.5°~30.17°N), where it descends along the southeastern margin of the Tibetan Plateau, which is of great significance for exploring the role of tectonics in controlling river incision at regional and local scales.
Methods This study analyzed the river profile of the Yunlong−Chaya tributary and calculated the channel steepness and incision amount within and below the knickzone and reconstructed the river spatial patterns.
Results The results indicate that most tributaries are in a transient state with one or two knickpoints. The knickpoint recovery suggests an incision range of 50~2700 m and northward increasing trend. At the same time, the knickpoint elevation and mean channel steepness index of tributaries also exhibit a comparable northward increase. The incision rates derived from previous studies based on river terraces along the main channel of the Lancang River exhibit spatial variations that are similar to the regional erosion rates on the million−year timescales.
Conclusions The spatiotemporal variation of the erosion rates along the Yunlong−Chaya reaches indicates that tectonics processes play a crucial role in shaping the landscape of southeast Tibet. In addition, the spatial consistency of incision depth, knickpoint elevation, and mean channel steepness index reveals that the tributaries of the Lancang River within the knickpoint zone have undergone episodic incision, upstream propagation, and multi−phase responses driven by tectonic uplift, further indicating that river evolution is highly sensitive to tectonic activity.
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