Comments on wave-induced behavior of a coastal mud

Abstract

The need for the prediction of phenomenal attenuation of sea waves as they approach mud-laden shores has led over the past decades to both analytic and numerical modeling of wave-mud coupling. A feature common to most analyses has been the use of canonical relationships relating stress to strain in mud, with time-independent coefficients in site-specific cases. For cohesive mud from the Atchafalaya River Delta along the Gulf of Mexico coast of Louisiana, laboratory work is described using a rheometer and a wave flume to highlight short-term and long-term responses of elastoviscoplastic mud to waves. Short-term may amount to perhaps no more than a few minutes, whereas tens of minutes or longer may be characterized as long term. For short-term response, a simple physical framework is used with rheometric data in preference to a mechanistic model to estimate the thickness of the dissipative mud layer formed by waves, an important parameter commonly deduced by model tuning against measured wave attenuation. In the long-term, characteristically time-dependent rheological parameters have an asymmetric, thixotropic response to the imposition and relaxation of stress. As the thixotropic timescale is commensurate with coastal storms, interpretation of wave attenuation predicted from short-term modeling must be treated with caution in prototype application.