Effect of Tide and Wave Characteristics on Nearshore Morpho- and Hydro-dynamics

One of the most important factors that govern the flow patterns and thus sediment transport is oceanic forcing energy. This energy is related to the wave and tide characteristics (viz., wave height, wave angle, and tidal range). In this study, nearshore hydro- and morpho-dynamics are investigated numerically under different oceanic forcing characteristics. In the numerical experiments, the Xbeach and Delft3D models were combined and used to solve the 3D Navier-Stokes equations for incompressible flow. The sediment transport module simulates both suspended-load and bed-load transport of non-cohesive sediments. A series of numerical experiments was performed for a range of control parameters. For each case, foreshore bathymetry changes and the overall morphological response were simulated in cross- and alongshore directions. In general, increasing the wave height causes a steady increase in the level of the peaks of eddy viscosity, turbulence kinetic energy (TKE) and wave set-up. TDR is very variable and strongly depends on incident wave height but also on other parameters such as tidal range and longshore current magnitude. As wave obliquity increases, the maxima in eddy viscosity, TDR, TKE and wave set-up are shifted onshore, in relation to the existence of an intertidal bar. The increase in obliquity enhances the longshore current, which in turn enhances bar formation. Therefore, the change in beach profile modifies the location of the maximum energy dissipation. Increasing the tidal amplitude reduces the peaks in eddy viscosity and TKE and spreads them towards the shore. The numerical results showed that, with increasing wave height or decreasing wave angle, there is an increase in the change in foreshore profile, berm size and volume of transported sediments. Maximum sediment transport/concentration takes place near the breaking area, and then decrease towards the shore. The results showed that for the tidal case, a very small volume of material was transported and did not cause considerable changes in the beach profile. This is because, under tidal forcing, TKE, flow velocity, and energy are low during both flood- and ebb- tide, and sediment resuspension is less. However, simulations that neglect the effects of tides are unable to reproduce accurately beach evolution when waves are present.