Hydrodynamic and sediment suspension modelling in estuarine systems - Part II: Application to the Western Scheldt and Gironde estuaries

Applications of the 3D-baroclinic numerical model described in Part I of this paper were performed in the Western Scheldt (The Netherlands) and Gironde (France) estuaries. Simulations provide an insight into cohesive sediment transport and its dependency on 3D flow features. In the Scheldt estuary, non-linear processes associated with the geometry of the estuary and the vertical profile of horizontal velocity generate effective upward and downward movements promoting vertical mixing. These movements are responsible for the small vertical gradient of density. The sediment distribution is characterised by two zones of high concentration associated with the different characteristics of bottom sediments. The maximum turbidity is not directly associated with the density currents but mainly with the variation in estuarine width and its effects on flow field. In the Gironde estuary, the vertical gradient of the residual velocity is small. Until pk70, the flow is seaward over the whole cross-section. Between pk70 and the estuarine mouth there is a large eddy with seaward flow in the northern channel. The inward velocity is stronger near the surface, suggesting that the residual flow is associated with the tidal movement and, to a less extent, with the density. The simulation of cohesive sediment transport accounting for the effects of the density current shows that the location of the turbidity maximum is strongly controlled by the fluvial discharges. (C) 1999 Elsevier Science B.V. All rights reserved.