Turbulent exchange of fine sediments in a tidal channel in the Ems/Dollard estuary. Part II. Analysis with a 1DV numerical model

In-situ high-frequency measurements were made of velocities and suspended sediment concentrations at three levels close to the bed at one location in a tidal channel during a few tidal cycles in June and August 1996, as described in a companion paper. In the present paper time series of mean velocities, suspended sediment concentrations and turbulence properties obtained are analysed with a one-dimensional numerical model. The model comprises a k–ε turbulence model that allows for the investigation of possible effects of density stratification on the vertical exchange processes. Computational results indicate that rapid settling of suspended sediment towards slack water can be explained from stratification effects. They also indicate a locally limited availability of sediment from the bed during high flow velocities. A sediment settling velocity of about 0.5 mm/s was found from fitting the computed vertical sediment fluxes to the measured ones. Attempts, using algebraic relations, to establish a possible dependence of settling velocity on suspended sediment concentration or turbulence level were not successful.