Numerical modeling of the influence of tides on cross-shore sediment dynamics of dissipative beaches under moderate wave conditions

摘要

The influence of tides on cross-shore sediment dynamics of a longshore-uniform beach is studied by means of a 1D numerical model (XBeach). The model is modified to include longshore tidal currents induced by water level gradients. The effect of tides on cross-shore sediment dynamics is quantified by analyzing the change in suspended sediment concentration, sediment advection velocity, and sediment transport. The effect of tides is decoupled into its two main components, i.e., water level fluctuations and tidal currents. Water level fluctuations modulate wave orbital velocities, wave-averaged currents and sediment advection velocity, therefore affecting both resuspension of sediments and cross-shore sediment transport. Tidal currents favor tidally-averaged sediment resuspension due to the increase in applied shear stress on the bed. The effects of water level fluctuations and tidal currents on sediment dynamics vary in the cross-shore direction: tidal currents increase sediment resuspension in deeper water depth, while water level fluctuations control the changes observed in shallow waters. In shallow waters, tidal amplitude is a good indicator of the influence of longshore propagating tides on the cross-shore sediment dynamics of a uniform beach, while in deeper waters, tidal wavelength also plays an important role. The model predictions are able to capture the trends observed in field measurements.