The sediment dynamics on the lower Scheldt vary seasonally through differences in sediment properties (fall velocity, erosion rate) and hydrodynamics (discharge, water level set-up/set-down, wave height). Both the variable sediment dynamics and the hydrodynamics probably influence the sediment transport into the Deurganckdok. The effect of seasonally varying hydrodynamics and sediment properties on the sediment dynamics of the Scheldt and on sediment transport into the dock are analyzed with the 3D mud model and the LTV mud model.
The most important seasonal variation is the downstream shift of the turbidity maximum and higher sediment concentrations during winter. The downstream shift of the turbidity maximum results from an increased fresh water discharge, but possibly also from the increased erosion rates in winter. The sediment concentrations are highest in winter due to increased erosion rates and higher sediment concentrations at the downstream and upstream reaches of the lower Sea Scheldt (both caused by increased wave action and higher discharge, respectively).
Sediment transport into the Deurganckdok is mainly seasonally influenced by variations in the sediment concentration on the Scheldt, and is therefore highest in winter. The transport into the dock is only marginally influenced by seasonal variations in exchange flows due to high discharge and water level setup or setdown, because their effect on the magnitude of exchange flows is low, and the a new equilibrium is rapidly attained. Given the low frequency of occurrence of these events, the contribution of modified exchange flows to yearly sedimentation in the dock is marginal.
The effect of the dock on the Scheldt is a local decrease in sediment concentrations, but the large-scale sediment transport patterns in the Scheldt are not substantially influenced. An additional effect is an increase in salinity upstream of the Deurganckdok resulting from increased mixing rates on the Scheldt near the Deurganckdok.
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