Quantitative analysis of the macro-geomorphic evolution of Buyuan Basin, China

摘要

Buyuan River,the largest tributary within the Chinese Lancang-Mekong River region downstream of the Jinghong Dam,plays a crucial role in river function and ecosystem service of the Lancang-Mekong River.The geomorphic evolution of a basin exerts a key control on riverine sediment input and transport.In this study,the geomorphic characteristics of Buyuan Basin are analyzed using morphological parameters,hydrodynamic parameters and the stream power river incision model.The results show that:1) The slight north-south difference of channel density is most likely due to lithology and independent of tectonic activity and climate.2) The weak tectonic activity and the low hypsometric integral (HI) value suggest that the macroscopic landform condition limits erosion and sediment production.3) The logarithmic longitudinal profile of the main channel defends that the upstream sediments generated by erosion are easily deposited in the downstream channel,rather than being transported directly into the Lancang-Mekong River.4) Approximately 74％ of the reaches have annual average stream power less than 500 W·m-1.The narrow variation ranges of stream power in 50％ of the river channel indicate relatively stable hydrodynamic environment.5) Stream erosion and tectonic activity make the longitudinal profiles of the main channel and most tributary channels unstable.The wide range (between 22.01 and 45.58 with θ=0.43) of steepness index (ksn) of longitudinal profiles implies differential uplift in the basin.