Factors Controlling Variation in Sediment Transport at Nhat Le Estuary

Knowledge of sediment transport in an estuary is essential for addressing many issues ranging from morphodynamics and water quality. Nhat Le estuary is the largest estuary with respect to river discharge in Quang Binh province, Vietnam and plays very important role in providing a safe navigation to fishing and recreational. In the tidal shallow-water estuarine area with high seasonal variation of river discharge, the sediment transport in Nhat Le estuary are complex. At the estuary, strong variation of the erosion and deposition processes have been occurring at the high frequency raise a concern of what reason can be attributable to the process. While a number of studies have explored the hydrodynamic regime in Nhat Le estuary, few have attempted to conclude which factor predominantly contribute to sediment transport and river mouth morphology in the area. To better understand we used a high-resolution hydrodynamic model (Delft3D) fully coupled with wave and sediment transport models to examine the importance of the principal factors controlling the morphology in the Nhat Le estuary. We conducted field experiments during both dry and wet seasons in 2018 to collect water levels, currents, waves, and sediment samples. The variation of the morphology in spatially and at single points under different scenarios are discussed. Model predictions suggest that wind-wave have significantly influence on sediment transport and river morphology with the effect accounted for nearly 95% whereas river discharge and tide play minor role.