Scalar transport by propagation of an internal solitary wave over a slope-shelf

Abstract

Internal solitary waves (ISWs) of depression are commonly found in the coastal environment and are believed to re-suspend sediments in coastal regions where the waves break. In this research, the direct numerical simulation is used to study the scalar transport induced by the ISWs of depression propagating over a slope-shelf topography. The scalar in this paper is considered to represent the concentrations of very fine suspended solids or pollutants. Vortices are observed from the numerical results at the bottom boundary layer on the slope during the ISW shoaling process, resulting in a scalar transport. All incident ISWs of depression are observed to produce a waveform inversion on the shelf. The scalar transport from a slope to a shelf is the consequence of the combined vortices at the bottom boundary layer and the overturning of the ISWs of depression, and the latter was commonly ignored in previous studies. This study shows that the ISW-induced scalar transport consists of the following four stages: the slip transport, the wash transport, the vortex transport, and the secondary transport. A dimensionless time scales of the four stages are calculated, and the beginning times of the wash transport and the secondary transport are found to be uncorrelated with the slope gradients, taking values of 1.26, 4, respectively.