Parameterization of Wave Attenuation in Muddy Beds and Implication on Coastal Structures

Abstract

The complex interaction between surface waves and muddy sea bottom is pivotal for wave evolution studies in coastal regions. Considerable absorption of wave energy resulting in decreased wave height had been observed in numerous geographical locations which include countries like China, India, South Korea and Louisiana (Gulf of Mexico), USA. Strong dissipative effects of cohesive sedimentary environments on waves are well known, but little understood. The spectral action balance equation used in numerical wave modeling expresses evolution of wave energy as a function of frequency and direction, balanced by various source and sink mechanisms. In this research paper, we propose an improved parameterization of bottom induced wave attenuation which is an inherent limitation in the existing state-of-the-art third generation wave models. We explain through theoretical formulations wave propagation and attenuation in heterogeneous environments, where significant wave damping over entire wavelength is observed in bottom strata having mixture of sand with mud (hereafter referred to as slurry). In the context of engineering relevance, such a mixture is termed “slurry” commonly referred in dredging technology. Hence, in this work we propose and incorporate a parameterization form of wave attenuation in the action balance equation which accounts for dissipative mechanism for slurry dominated bottoms. The attenuation coefficient is thereby determined and a comparison is made with the theoretical formulation due to slurry and sand for a one-dimensional case. The study also addresses implication of such wave attenuation on coastal structures.