Assessment of risks associated with development of river meandering under climate change using a physics-based free-meandering model

Abstract Recent increases in heavy rainfall events, which may have resulted from climate change, have caused various natural water- and sediment-related disasters. A typical sediment-related disaster in a steep gravel-bed river is extreme bank erosion and subsequent meander development, damaging residential areas and infrastructure along the river. Assessing the bank erosion rate and its future changes under climate change is essential to prevent such severe disasters. Here, we propose a simple but useful framework for this purpose using a physics-based numerical model of free meandering and a large dataset of flood hydrographs generated from climate and runoff models. First, numerical experiments on meandering development were conducted using a two-dimensional morphodynamic model of free meandering. The results indicate that meander dynamics could reach a dynamic equilibrium state under several hydraulic and channel geometry conditions, and the characteristics of the simulated meandering channel were reasonably consistent with the field data. The meander amplitude of this state was positively correlated with the steady discharge; therefore, the increase in flow discharge may have an important effect on river dynamics under climate change. To quantify this effect, we combined a simple predictor of meander amplitude derived from a numerical experiment with a flood hydrograph dataset for current and future climatic conditions. The results suggest that the meander amplitude increased significantly for the same probability of occurrence; therefore, the risk of riverbank erosion due to river meandering will increase significantly under future climate conditions.