Experimental investigation of sediment resuspension beneath internal solitary waves of depression

Abstract

Internal solitary waves (ISWs) of depression are common features of coastal environments and believed to resuspend sediments where they shoal. In this study, the sediment resupension process associated with ISWs propagating over a flat bed was investigated in the laboratory. The first-ever profile measurements of the three-dimensional instantaneous velocity field beneath the ISWs revealed that resuspension occurs during burst like vertical velocity events, which lift sediments into the water column, in the adverse pressure gradient region beneath the trailing part of the wave. Resuspension was not observed when the wave-induced viscous bed stress was maximal directly beneath the ISW trough. Prediction of wave-induced resuspension was, therefore, unsuccessful using a traditional viscous bed stress-based Shields diagram. A parameterization for ISW-induced resuspension is proposed as a function of the maximum instantaneous vertical velocity in the bursts wmax. Here we have replaced the viscous bed stress with τISW=ρ2wmax2, where τISW is the instantaneous resuspending bed stress and ρ2 is the near-bed fluid density. From these results, it is possible for field-oceanographers to predict the occurrence of ISW-induced resuspension from the bulk wave and stratifications characteristics in a two-layer stratification. Further research is required to extend the parameterization to larger Reynolds numbers at field-scale. Key Points: Lab experiments reproduce solitary wave-induced resuspension The instantaneous 3-D velocity field under the waves is measured A parameterization for resuspension is developed