Experimental investigation of instability of fluid mud layer under surface wave motion

Abstract

Motivated by environmental impacts of surface-wave induced mixing of fluid mud with clear water in nearshore areas, this paper presents quantitative measurements of excitation of interfacial waves over a bed mud layer by a surface wave in a wave flume. After an initial fluidization process, a quasi-standing interfacial wave comprised of four interfacial waves was observed at the interface as a result of a resonant wave interaction with the surface wave. The interfacial waves were subharmonic to the surface wave and traveled at the maximum possible angle from it. The growth rate and kinematic properties of the interfacial waves were measured, and good agreement with theoretical predictions of a two-layer interaction model was obtained. It was found that excitation of these waves was highly dependent on the surface wave height and fluid mud viscosity. Furthermore, thickening of the lutocline layer as a result of resuspension of fluid mud highly influenced the wavelengths as well as the damping rate of the interfacial waves.