Dynamic characteristics of sandbar evolution in the lower Lancang-Mekong River between 1993 and 2012 in the context of hydropower development

Hydropower development activities in the Lancang-Mekong River basin have become increasingly intense in recent decades, with potential impacts on river landforms and even the evolution of the estuarine delta. River sandbars are very sensitive to changes in runoff and sediment concentration; therefore, to analyze the dynamic characteristics of sandbar evolution in the lower Lancang-Mekong River (i.e., Mekong River), this study compared the dynamic parameters of the river before and after dam construction, using multiple regression equations based on data from historical remote sensing imagery, runoff, channel width, and gross domestic product (GDP) per capita. The results show that the sandbars have shrunk significantly since 2005, being consistent with the shrinkage of the Mekong delta, which suggests that the shrinkage of the two landforms may be dominated by the same factors. The direct factors causing this shrinkage phenomenon are a relative increase in erosive forces and a decrease in sediment sources simultaneously, which is specifically due to the slight increases of stream power and runoff shear stress, damming, sand mining activities downstream, urbanization and others. However, compared to climate changes, GDP-related human activities that manipulate these direct factors are likely a more significant driving force behind the changes in sandbar size. When the GDP per capita of the downstream basin was less than 1,614 USD/yr, the increase in the intensity of human activities led to an increase in sandbars. Conversely, when the GDP per capita exceeded 1,657 USD/yr beginning in 2005-2006, the sandbars shrank. This study reminds us that the impact of human activities on the evolution of downstream fluvial landforms is increasing in the lower Mekong River.