Coastal hydrodynamics II

The statistical distribution of waves in short-crested seas is critical for the design of coastal structures, not least because large, breaking waves are known to induce significant wave loads. Despite recent advancements, discrepancies remain in the statistical description of crest heights in finite waters. These are particularly highlighted in cases where strong nonlinear effects/wave breaking are prevalent. The present work utilises a large experimental dataset of random simulations of short-crested seas to provide further insights into those mechanisms. Specifically, a novel method to identify waves that undergo nonlinear amplifications and wave breaking is developed. This is used to calculate the associated energy gain/dissipation per wave. A modelling suite is proposed to describe the probability of wave breaking and associated dissipation, which is then converted into a mixture model to recover crest height statistics. The success of the proposed approach is demonstrated through comparisons between model predictions and measurements.

Nature-based flood defences receive increasing interest as a viable option for improving flood safety worldwide. A contemporary case is using the ability of saltmarshes to attenuate waves during storm conditions for strengthening coastal flood defences. To ensure a long-term reinforcement of flood protection, it is important to understand the erosion mechanisms of saltmarshes during storms. One of the critical locations for erosion is at the transition between the saltmarsh and the bare mudflat, often characterized by a vertical step or cliff. However, wave-induced hydrodynamics that controls the (mass) erosion at the saltmarsh cliff are not fully understood. Also the role of saltmarsh vegetation on these near-cliff hydrodynamics are not clearly quantified. In this research, we present high-resolution measurements of wave-induced hydrodynamics at a saltmarsh cliff by using Particle Image Velocimetry performed in a scaled wave flume experiment.