Application of Wave-current coupled Sediment Transport Models with Variable Grain Properties for Coastal Morphodynamics: A Case Study of the Changhua River, Hainan

Abstract. This study presents an integrated sand transport model that accounts for both wave and current actions, along with non-constant grain properties, to investigate sediment dynamics in the lower reaches of rivers. Taking the downstream and estuary of the Changhua River in Hainan Island as a case study, topographic data and sediment sampling were conducted in the field, complemented by remote sensing techniques. The model was rigorously validated using theoretical and empirical methods, demonstrating excellent agreement with observed suspended sediment concentrations at the Baoqiao Station. The findings indicate significant sediment deposition in the estuary and lower reaches of the Changhua River, influenced by a combination of hydrodynamic conditions and geological settings. Deposition in the estuary is primarily affected by the northeast-southwest coastal currents and wave action, while deposition in the river channel is associated with river constriction and variations in flow velocity. The models and methods developed in this study provide a scientific basis for sediment management and coastal evolution in similar downstream riverine environments and discuss the feasible scheme of sediment control in the downstream of Changhua River.