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 introduces an integrated sand transport model that considers wave and current actions alongside variable grain properties to explore sediment dynamics in river deltas. The research delves into a case study of a river delta region, examining sediment transport over a substantial stretch of the river's lower course. The study incorporates topographic data, sediment sampling, and remote sensing to validate the model against observed suspended sediment concentrations at a key monitoring station. The results reveal substantial sediment deposition in both the estuary and lower reaches of the river, influenced by hydrodynamic conditions and geological settings. Deposition patterns in the estuary are primarily driven by coastal currents and wave action, while river channel deposition is linked to river constriction and flow velocity variations. The study demonstrates that the residual current in the region consistently flows towards a nearby bay, suggesting that sediment in the lower reaches of the river will be directed by this residual flow. The study underscores the pivotal roles of current and wave action in sediment transport within a multi-branched estuary characterized by low sediment concentrations, which can inform coastal management and environmental planning.