Study on the Vertical Distribution Characteristics of Suspended Sediment Driven by Waves and Currents

Abstract

Port coasts are affected by waves and tidal currents, and sediment continues to silt up, leading to a reduction in the depth of water in the channel, blocking the channel and seriously affecting the safe operation of ports. The main cause of sediment deposition in ports is suspended sediment transport, and the characteristics of the vertical distribution of suspended sediment concentrations are the embodiment of the suspended sediment transport law. This paper is divided into three parts to study the vertical distribution characteristics of suspended sediment concentrations. Firstly, the shortcomings of the traditional diffusion model were analysed by using the finite mixing theory (FMT); secondly, the sediment mixing length coefficient κs model was introduced and combined with the sediment group settling velocity model to establish the vertical distribution model of suspended sediment concentrations under wave–current; finally, the effects of various factors on the vertical distribution of the suspended sediment concentration were investigated. The results show that the model in this paper has the characteristics of “low variance and low bias”, which solves the problem that κs is difficult to determine. When the model κs < κs′ (κs′ = 0.4), the concentration of suspended sediment predicted by κs′ is overestimated, and vice versa. As the sediment concentration increases, the interaction between particles increases and the vertical distribution of the suspended sediment concentration shows the pattern of “small top and large bottom”. The larger the particle size, the greater the sedimentation rate of the suspended sediment, and a large amount of sediment will be suspended near the bottom without mixing. The higher the wave height, the stronger the boundary layer turbulence and the movement of the water particles’ trajectory, and the smaller the difference in sediment concentration between the bottom and the sea surface.