Controls on geomorphic characteristics of the Xiaohei River basin in the upper Lancang-Mekong, China

Understanding the evolution of the fluvial geomorphology in an orogenic belt provides valuable insight into the relationship between upper crustal deformation and surface processes. The upper Lancang-Mekong River is in an area experiencing both uplift and erosion. The related processes provide a steady sediment supply to the lower reaches of the river and play an important role in the regional environmental changes. The Xiaohei (Weiyuan) River Basin is an important sub-basin in this area, which is characterized by large-scale topographic fluctuations, active tectonics and erosion, and anthropogenic activities. These different factors introduce numerous complexities to the local surface processes. In this study, we investigate and quantify the controls of geomorphic evolution of the Xiaohei River Basin. We located and mapped the main knick-zones within the channels and examined the main genetic factors, such as faults and stratigraphic differences. The results show that the areas with the lowest uplift rates are characterized by a low steepness index and are located in the southeastern part of the basin. The stream power of the mainstream increases downstream, with an average value of ~122 W/m. The erosional activity of the various stream channels is intense. Overall, the basin tends to expansion, with only local instances of inward contraction. Our analysis confirms that a number of the geomorphic evolutionary characteristics of the Xiaohei River Basin are transient. In addition, the future potential for the increasing the number of dams and the hydropower development in the basin may weaken the expansion trend of the basin over a long period of time.