Tidal effects on the bulge region of Changjiang River plume

A three-dimensional hydrodynamic model is developed to investigate how tide affects the bulge region of the Changjiang River plume. In the absence of tide, the plume bulge exhibits multi eddies and grows with time. In the presence of tide, however, the bulge is well organized. Strong variation of turbulent mixing over the spring-neap tidal cycle causes periodic detachments and ejections of a plume patch from the river mouth. The detachment occurs during the neap to spring transition when tidally generated turbulence is strong enough to break down stratification in the inner shelf region near the mouth of Changjiang River estuary. As a consequence, the Changjiang River plume moves downstream as a series of low salinity patches. This detachment process occurs regardless of the river discharge conditions. Due to oscillating tidal currents in the Changjiang estuary, the freshwater outflow from the river mouth shows moderate (about ±20%) fluctuations around the river discharge over the spring-neap tidal cycle but large fluctuations (about ±5 times) around the river discharge over the flood-ebb tidal cycle. However, they only produce minor effects on the plume structure over the adjacent shelf.