Response of mud shore profiles to waves.

摘要

The concept of a spatially uniform rate of wave energy dissipation, dominated by viscous dissipation due to wave-induced motion of the soft bed, has been used to develop an analytic model of mud shore profile geometry. In the derivation, exponential wave height decay with distance and shallow water linear wave theory have been used in the wave-averaged energy conservation equation with normal wave incidence. The derived analytic profile is capable of predicting both concave-upward (erosional) and convex-upward (accretionary) nearshore mud profiles. The modality of profile change is dependent on the profile-averaged wave attenuation coefficient, {dollar}bar ksb{lcub}i{rcub}{dollar}, which characterizes the fluidization potential of mud. The parameter {dollar}bar ksb{lcub}i{rcub}{dollar} is shown to be a function of mud rheology, which, in turn, depends on the incident wave height. A high {dollar}bar ksb{lcub}i{rcub}{dollar} indicates the presence of a thick fluid mud layer; transport of the fluid mud elsewhere leads to an erosional profile. Conversely, a lower {dollar}bar ksb{lcub}i{rcub}{dollar} implies low wave height and an accretionary profile. By varying {dollar}bar ksb{lcub}i{rcub}{dollar}, the analytic profile is shown to reproduce the varying shapes of mud profiles from several field sites. Comparison of best-fit {dollar}bar ksb{lcub}i{rcub}{dollar} with that obtained from measured wave height decay in two field applications also shows close agreement.; Profile evolution is then simulated using a closed-loop approach whereby the analytic profile shape serves as the target profile toward which an initial, non-equilibrium profile eventually converges under constant wave forcing. The governing dynamic equation for cross-shore sediment transport, together with the volumetric sediment conservation equation, are numerically solved for transient profiles using an implicit finite difference formulation. The profile evolution model is shown to reproduce noteworthy features of the observed seasonal change in profile shape along a muddy coastline within the Southwest Louisiana chenier plain.; A laboratory investigation using a sunken flume with clayey shore profiles subjected to monochromatic wave condition was conducted. Comparison of the best-fit {dollar}bar ksb{lcub}i{rcub}{dollar} for a profile at the end of the test run to that calculated from the measured wave height envelope is shown to yield fairly close agreement.