An analytical model of the equilibrium distribution of suspended sediment in an estuary

An analytical solution of the equilibrium distribution of suspended sediment concentrations (SSC) in an estuary along the longitudinal axis is extended to include variable width. A turbidity maximum is formed at the convergence of fluxes from freshwater discharge and (vertically well mixed) salinity gradients. Simple scaling relationships control the longitudinal distribution of SSC and depend upon model parameters such as the applied salinity field, depth, width, freshwater discharge, settling velocity, eddy viscosity, and horizontal dispersion. These scaling relationships agree well with turbidity data from the Ems estuary. The modelled dependence of the SSC distribution on settling velocity (grain size) causes particles with a small settling velocity to be found preferentially in the outer estuary, while particles with a large settling velocity (large grained sand, cohesive sediments) are trapped in the turbid zone.