Transport and deposition of high-concentration suspensions of cohesive sediment in a macrotidal estuary

A width-averaged two-dimensional (2-D) model and a three-dimensional (3-D) model have been developed for the Jiaojiang estuary which is a highly turbid and macrotidal estuary. The sediment-induced buoyancy effects and the consequent turbulence damping effects have been taken into account in these models. It is possible to consider the upper suspensions and fluid mud as a whole, without empirical exchanges between these two compartments, as in the so-called continuous approach. The Princeton ocean model (POM) with a generalized sigma-coordinate system has been used as the hydrodynamics module of the 3-D model with improvements on advection schemes for scalar variables, introducing the drying and flooding algorithm and the additional capacity to deal with the non-Newtonian effects of high-concentration mud suspensions. Simultaneous currents and SSC (Suspended Sediment Concentration) time series data from several elevations at a mooring site and from ship-born observations over a tidal cycle in April 1991 enable the calibrations of these models. From the simulations and observations, some important findings have been obtained. The effective hydrodynamic drag is reduced in the very turbid environment. Under conditions of strong stratification due to sediment, the overall hydraulic roughness will be further decreased. The total mass of suspended sediment in the estuary is around 1.2 × 106 tons. The asymmetry in tidal currents drives the outer sediment to enter the estuary during the simulated period. The magnitude and location of turbidity maximum vary in the tidal cycle. The SSC, salinity and current have obvious longitudinal variations, while they also have cross-channel variations. The lutocline almost occurs over the entire cycle except during the period around high water slack. The fluid mud generally concentrates in the deep portions of estuary and in the shallow zone separating the estuary and Taizhou Bay.