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[1] Effects of tides on the Changjiang River plume are investigated using a numerical model of the East China and Yellow Seas. In the absence of tides, the buoyancy-driven coastal current downstream of the river mouth is a surface-trapped plume attached to the coast. In the presence of tides, however, the plume shifts away from the coast and features a bottom boundary layer. The freshwater transport by the coastal current accounts for only 35% of the Changjiang River discharge without tides but increases to 80% with tides. Tidal currents stabilize the plume bulge near the river mouth and force the plume water to move in the direction of tidal currents, thus increasing the downstream freshwater transport. In contrast, tidal residual currents are weak and make little contributions to the total freshwater transport. Tidal mixing reduces the plume's buoyancy but increases its thickness so that the freshwater transport is insensitive to the strength of turbulent mixing. Volume transport in the tidal-affected buoyancy coastal current exceeds the river discharge by 4 to 12 times, as opposed to 2-3 fold amplification in the plume without tides. Tidal mixing between the plume and ambient shelf waters produces higher salinity classes in the plume so that the volume flux in the downstream coastal current increases to discharge the freshwater released from the Changjiang River.

a b s t r a c tWave-current interaction over the Texas-Louisiana shelf, and its effects on the dispersal and mixing of the Mississippi-Atchafalaya river plume, have been investigated using the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modeling System. The modeling system is driven by realistic wave and current conditions at the open boundaries and high frequency1-D wind measured from a nearby meteorological station. Skill analysis demonstrates that the model reproduces the wave and salinity fields reasonably well. Waves over the Texas-Louisiana shelf are dominated by locally forced wind seas, and generally propagate in the same direction as the winds. Investigation into the spatial differences in the effect of waves reveals two distinct dynamical regions: the Chenier shelf, the shelf region extending roughly offshore from Sabine Lake to Vermilion Bay, and the Louisiana Bight, the region between the Mississippi Delta and Terrebonne Bay. A variety of model runs are performed, where specific wave processes are either included or excluded, in order to isolate the processes acting in different regions. The Chenier shelf is mainly affected by wave enhanced bottom stress, whereas the Louisiana Bight is mostly affected by the surface wave induced mixing and 3-D wave forces. The wave enhanced bottom stress suppresses cross-shore exchange, and acts to trap more freshwater in the nearshore regions shallower than 50 m over the Chenier shelf. Wave enhanced bottom stress plays only a minor role in the Louisiana Bight, where the surface-trapped Mississippi plume rarely feels the bottom. The surface intensified wave mixing and 3-D wave forces reduce the surface salinity and weaken the stratification in the region associated with the thin recirculating Mississippi plume in the Louisiana Bight. Model results indicate that the surface wave mixing, the 3-D wave forces, and the wave bottom stress exhibit little interaction over the Texas-Louisiana shelf. Finally, we have demonstrated that the one-way coupling is capable of resolving the majority of wave effects over the entire shelf if the seasonal scale is of interest.

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