Wave shape prediction in complex coastal systems

Abstract

When waves propagate towards the coast, nonlinear interactions occur under the influence of decreasing water depth and variable ambient currents. This changes the initially harmonic wave shape into a nonlinear wave shape due to the presence of bound waves accompanying the freely propagating primary waves. The nonlinear wave shape ranges from skewed waves with steeper crests and flatter troughs to asymmetric waves where the wave front has pitched forward creating a saw-tooth wave shape at breaking. Analogous to the nonlinear surface elevation, also the near-bed orbital wave velocity is nonlinear. This results in a wave-shape driven sediment transport, generally directed in the direction of wave propagation. For accurate predictions of the sediment transport, it is thus important to know the wave shape. This is especially important in complex coastal systems with strong variations in bathymetry where wave-induced sediment transport gradients affect the subsequent morphological evolution. Therefore, this thesis focuses on measuring and modelling of the nonlinear wave shape....