Axial wind effects on stratification and longitudinal sediment transport in a convergent estuary during wet season

The Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system was used to examine axial wind effects on vertical stratification and sediment transport in a convergent estuary. The model demonstrated that stratification dynamics in the upper estuary (Kelvin number <1; Ke = integral B/root g'hs) are dominated by longitudinal wind straining, whereas the dominant mechanism governing estuarine stratification in the lower estuary (Kelvin number similar to 1) is lateral wind straining. Barotropic advection contributes to seaward sediment transport and peaks during spring tides, whereas estuarine circulation causes landward sediment transport with a maximum during neap tides. Down-estuary winds impose no obvious effects on longitudinal sediment flux, whereas up-estuary winds contribute to enhanced seaward sediment flux by increasing the tidal oscillatory flux. The model also demonstrates that bottom friction is significantly influenced by vertical stratification over channel regions, which is indirectly affected by axial winds. Plain Language Summary Winds have significant impacts on estuarine density stratification and sediment dynamics, which may affect water quality, siltation of navigation channels, and the overall health of estuarine ecosystems. Despite this great influence, the mechanisms controlling stratification and sediment transport by axial winds in a convergent estuary have not received adequate attention. Here we use a coupled ocean model system to examine axial wind effects on vertical stratification and sediment transport in a convergent estuary. The ocean model reproduced the observed water elevation, velocity, salinity, and sediment concentration well and shows that the density stratification in the upper bay is mainly controlled by longitudinal wind straining, whereas that in the lower bay is dominated by lateral wind straining. Up-estuary wind enhances seaward sediment transport by increasing the tidal oscillatory flux, whereas down-estuary wind has a limited effect. Through this study we advanced our understanding on stratification and sediment transport in a convergent estuary and noted that winds have great influence on tidal oscillatory sediment transport, which may change the sedimentary budget in an estuary.