QUANTIFIYING WAVE-INDUCED PRESSURES ON A SALTMARSH CLIFF: AN EXPERIMENTAL STUDY

Increased forcings on existing coastal flood defences due to sea level rise and an increase in storminess leads to a current challenge to reinforce coastal flood defences, such as coastal sea dikes. Conventionally, these structures are reinforced by increasing their height and thereby the total width of the structure. Aside an increase in costs, it reduces either landward usable area or seaward area, where intertidal mudflats and vegetated saltmarshes provide vital ecosystem services. An alternative can be found in actively including these foreshore/saltmarsh systems in the coastal protection scheme. During storm conditions, the inundated vegetation leads to higher energy dissipation than non- vegetated foreshores (Möller et al., 2014), while the induced shallower conditions also contribute to reduce the wave height at the toe of the dike. Hence, reducing the need for increasing the height of the dike itself. In order to actively include the saltmarsh within a long-term coastal protection system, the saltmarsh should be stable during various storm conditions. However, erosion at the saltmarsh cliff is not well understood. Wave-induced forcing at the cliff leads to failure of the exposed cliff, but a clear quantification of the complex, near-cliff flow and pressure distribution is lacking as well as a complete understanding of the underlying triggered failure mechanisms. In this research, we present high-resolution measurements of wave-induced hydrodynamics and local pressures at a saltmarsh cliff performed in a scaled wave flume experiment.