Numerical investigation of a sandbar formation and evolution in a tide-dominated estuary using a hydro-morphodynamic model

This paper presents a numerical study on 'sandbar' feature in a tide-dominated symmetrical funnel-shaped estuary using a hydro-morphodynamic model. A series of benchmark flows is simulated to demonstrate the capabilities of the model (e. g., well-balanced property, treating wet/ dry fronts, shock-capturing ability), and the good quantitative accuracy. Afterwards, the model is applied for systematic numerical case studies. The main geometrical parameters, the upstream and boundary conditions are specified with reference to the Qiantang River Estuary (QRE), where a giant 'sandbar' is well known. It is shown that a maximum turbidity zone forms due to interactions of the riverine discharge and the tidal flow. Strong deposition occurs in the maximum turbidity zone, whereas erosion occurs otherwise. This results in a sandbar of comparable magnitude and position with the observed 'sandbar' in the QRE. As the sandbar grows, a slight increasing trend followed by a rapid decreasing trend for the difference between high and low water levels is established. A larger riverine discharge leads to a sandbar more closer to the seaside, but effect of the seasonal discharge variation is limited. Erodibility of bed and seaside sediment input mainly influence the height of the formed sandbar.