Review of sediment yield, transportation, and trap in reservoirs in Lancang-Mekong River basin

The Lancang-Mekong River is one of the largest transboundary river shared by China and Southeast Asian countries. In recent years, the sediment issue in this large river has received extensive attention due to nutrient-rich sediment decreasing which is critical to ecological health, aquatic habitats, shipping, coastal erosion and agricultural and fisheries production. A wide range of studies on sediment yield, transportation and trapped by reservoirs are summarized. The main controversial topics include where the most sediment comes from, how to explain the abnormal relationship among suspended sediment loads observed along the mainstream, and the quantification of effect of human activities on sediment load change. There are five main issues unsolved, including unreliable observed sediment data in Lower Mekong River, weak basis of total sediment load of 160×10⁶ t/a, low spatiotemporal resolution in model simulation, insufficient study of the land use change impacts in recent decades and inadequate research on sediment except for suspended sediment. Several possible ways to overcome these difficulties are also discussed.