Laboratory study of instability-driven mixing of fluid mud under surface wave motion

Abstract

Motivated by the role of interfacial instabilities in sediment resuspension in coastal areas, this paper provides quantitative measurements of fluid mud density profile during motion of a surface wave over a muddy bed in a wave flume. Following a fluidization process, a quasi-standing interfacial wave grew owing to a resonant wave interaction with the surface wave. In the process, the quasi-standing wave reached a maximum amplitude and then approached a steady state. The long-time behavior of the resonantly generated interfacial wave and the changes in vertical density profile during wave motion were recorded. Increasing the surface wave frequency led to a higher initial growth rate of the interfacial wave within the experimental range, but the faster growth rate did not result in a larger final amplitude. The results show that excitation of the interfacial wave results in increasing water turbidity such that the water column becomes turbid in a matter of a few minutes. In general, the change in the fluid density profile is highly correlated with the quasi-standing interfacial wave amplitude during the resonant interaction. The amount of entrained mud particles into the clear water by the end of each experiment was determined. The ultimate amplitude of the quasi-standing interfacial wave was found to be a major factor in sediment resuspension.