Modelling the Dispersion of Dredged Material in Marine Environment Using Hydrodynamic and Sediment Transport Simulations in Tho Quang Port, Vietnam

Maintaining navigable port channels through dredging is crucial for maritime trade, yet offshore disposal of dredged material can impact the local marine environments. This study modeled the dispersion and deposition patterns of total suspended solids (TSS) resulting from the disposal of dredged sediments at an offshore site near Tho Quang Port, central Vietnam. An advanced coupled numerical modeling system integrating hydrodynamics, spectral waves, and sediment transport processes was developed using the MIKE modeling suite. Extensive field data was collected and used for model parameterization, boundary conditions, and rigorous validations, including bathymetry surveys, acoustic doppler current profiler measurements, tide gauge data, and sediment sampling/characterization like grain sizes, densities, settling velocities. Simulations over a 45-day construction period represented extreme scenarios under contrasting Southwest and Northeast monsoon conditions. The model results showed that the highest TSS concentrations, above 0.05 kg/m³, were restricted to an area within 12 km of the disposal location. However, the 0.015-0.02 kg/m3 contour extended further along the predominant northwest-southeast dispersion axis aligned with prevailing winds and currents, reaching 12-18 km. Seabed accumulation patterns showed a radially symmetrical cone with maximum thicknesses of 0.5 m proximal to the release site. The 0.1 m deposition footprint spanned 102-122 ha due to asymmetric sediment advection by the contrasting monsoon forcings. Key factors governing the dispersion and accumulation patterns included sediment characteristics, hydrodynamics (tides, currents, waves), wind forcing, and bathymetry. TSS plumes and sedimentation footprints were constrained, suggesting disposal impacts may be localized around the authorized site during operations based on the limited dispersion predicted. This study highlights the value of integrated numerical modeling for quantitatively forecasting the environmental impacts of dredged material disposal. Such predictive insights can guide monitoring programs, ecological risk assessments, and the development of mitigation strategies to balance infrastructure growth with environmental protection goals for coastal regions. Keywords: Submersion; enviromental modeling; sediment dredging; TSS dispersion; seabed occupation.