Modeling River Morphodynamic Process Using a Depth-Averaged Computational Model and an Application to a Mountain River

Abstract

Bank erosion is a dominant river morphodynamic process resulting in encroaching valuable farming land and channel migration. Prediction of bank erosion and channel migration requires understanding of the morphodynamics of the entire river system. Numerical modeling is an ideal method for this task. How-ever, models with full capabilities and applications on complex real-world problems are rare. In this study the finite element-based computational model, CCHE2D, and its flow, sediment transport, and bank erosion modules are introduced. The model is capable of simulating unsteady flows with nonuniform sediment transport and cohesive/non-cohesive material bank erosion. The effects of helical secondary current on sediment transport induced by flow curvatures are reflected in both bed load and suspended sediment formulations. This model is validated using multiple sets of experimental data and applied to bank erosion problems of the Chuoshui River, a real-world mountain river in Taiwan. Characterized by typhoon floods, steep channel slopes, and high sediment load and mobility, this river often exhibits a braided pattern consisting of multiple curved channels. Channel bed change and bank erosion caused by 10 years of typhoon floods in a selected reach have been simulated, and the computed bank erosion results agreed with the field observation.