Modeling investigation of suspended sediment transport in a tidal estuary using a three-dimensional model

This study presents an incorporation and application of a three-dimensional, unstructured-grid hydrodynamic model with a suspended sediment transport module in the Danshui-River estuarine system, Taiwan, and its adjacent coastal sea. The model is verified with data observed in 2010: water surface elevations, longitudinal velocities, salinities and suspended sediment concentration (SSC). The simulations agreed quantitatively with the observations. The validated model was applied to numerical experiments to investigate the formation of the estuarine turbidity maximum (ETM) and the influence of vertical mixing, different freshwater-discharge conditions and bathymetric change on suspended sediment dynamics in the main Danshui-River estuary. The model results reveal that the suspended sediment may be trapped in the deeper section of the river. Higher vertical diffusivity slightly increased SSC because of greater bottom stress during the ebb tide. Under extreme freshwater-discharge conditions, SSC increased considerably at both the surface and bottom layers of the water column, and ETM shifted its location upstream. When we change the bathymetry near the Guandu Bridge in our model, ETM extends its range a further 5.0 km from the river estuary because of higher velocity.