Long‐Term Simulations of Bar Dynamics in Compound Channels Under Climate Change

Abstract

The height of alternate bars in rivers can have a significant influence on riparian vegetation succession, sediment transport, and lateral erosion. Knowing and managing river channel responses under climate change requires predicting long‐term variations in bar height. Traditional linear models often struggle to accurately represent rivers with floodplains or highly nonlinear conditions. In this study, we incorporate equilibrium bar height and growth rate parameters derived from fully nonlinear 2D simulations into a linear model. This methodology integrates the impacts of floodplain inundation and secondary flow formation, providing enhanced precision compared with a traditional linear model. We apply this model to compound channels of different widths across a range of discharges, and our findings indicate that for a fixed channel width, bar height has a nonlinear relationship to the width‐to‐depth ratio (), with maximum bar heights when is between 20 and 30. We also use the model to investigate the potential impacts of altered hydrology due to climate change on bar characteristics. Under the climate change scenario, where the channel width remains constant (i.e., conditions where bank erosion is prevented by bank protection works), increased frequency of large floods reduces , and therefore increases the frequency of attenuation of bar height. However, intermediate flow discharges producing of 20–30 also increased for compound channels of larger width, causing the average bar height to increase under climate change for those channels. These results indicate that climate change may increase bar height depending on channel width, resulting in an increased risk of bank erosion and floodplain inundation.