Tide, turbulence and suspended sediment modelling in the eastern English Channel

Abstract

The present paper is concerned with modelling fluid and suspended sediment dynamics in a tide-dominated environment. The procedure consists of a one-dimensional vertical model driven by an oscillatory horizontal pressure gradient derived from a two-dimensional vertically integrated tidal model. The vertical model includes two linearised momentum equations for the horizontal velocity components and a series of advection–diffusion equations for concentrations of suspended sediment of specific size. Turbulence generated at the seabed is computed with the aid of a two-equation closure describing the time–space evolution of the turbulent kinetic energy k and of the dissipation rate of the turbulent kinetic energy ε (standard k− ε model). A mixed type bottom boundary condition for the sediment concentration equations is adopted to take into account downward fluxes at times of decelerating flow and slack waters. The model is applied to the eastern part of the English Channel. The tidal currents, turbulent kinetic energy and the total suspended sediment load predicted by the model are compared with field data collected in two sites. The vertical structure of these flow properties is fairly well predicted by the present model. Better results are found at the measuring point located farther from the coastline where advective terms can be reasonably neglected.