Field and modeling studies of fine sediment dynamics in the extremely turbid Jiaojiang River estuary, China

The Jiaojiang River estuary, China, is very turbid with depth-averaged suspended sediment concentration commonly exceeding 10 kg m(-3) at spring tides. An asymmetry of the tidal currents is caused by shallow water effects. This asymmetry generates, at spring tides, a turbidity maximum in the estuary near the salinity intrusion limit. The rates of erosion and deposition are controlled by the tidal currents and the constants in the equations for those rates were inferred from 12 days of data. A transient sediment layer forms at slack tide and is eroded at a threshold velocity of about 0.3-0.4 m s(-1) which is about half the value of the erosion threshold velocity of the consolidated sediment underneath. The data were used to calibrate a sediment dynamics model which was successful at reproducing most of the observations at spring tides. The model suggests that the bulk of the sediment in the estuary is imported from coastal waters. This sediment originates from the Changjiang (Yangtze) River which is located 200 km further North. The Manning's bottom friction coefficient is found to be smaller (by 30%) than that in non-turbid estuaries and this may be due to the presence of a fluid-mud layer near the bottom.