BREAKING-WAVE-DRIVEN SEDIMENT BYPASSING OF RIVER MOUTHS: MECHANISMS AND EFFECTS ON DELTA EVOLUTION

摘要

River mouths along sandy coastlines are influenced by alongshore transport of littoral sands. Here we simulate river mouth morphology under oblique wave approach with the numerical model Delft3D. Specifically, we study the mechanisms of alongshore sediment bypassing at river mouths. We find that bypassing rates are strongly dependent on river discharge and wave energy. River mouths deflect in the presence of littoral sediment transport when waves refract into the jet and subaqueous shoals. This wave refraction leads to a zone of low energy and sediment transport updrift of the river mouth, decreasing its ability to bypass littoral sediment. Because of this wave-refraction effect, the fraction of alongshore sediment transport that is bypassed can be explained by the ratio of jet momentum flux versus wave momentum flux. Quantifying environmental controls on river mouth morphology and alongshore sediment bypassing rates will give insight into the potential evolution of deltaic coastlines in a changing environment.