Stability of morphological cells to dredging-dumping activities
Zimmermann, N. (2009). Stability of morphological cells to dredging-dumping activities. MSc Thesis. Hydraulic Engineering Section, Faculty of Civil Engineering and Earth Sciences, Delft University of Technology: Netherlands. 72 + appendices pp.
The Westerschelde estuary in the South-West of the Netherlands displays two meandering flood and ebb channels separated by shoals. The system of flood, ebb channel and shoal between two channel crossings form a morphological cell. The stability of the serial cell system formed by the Westerschelde is important for the navigation route to the port of Antwerp. Wang and Winterwerp (2001) proposed a simplified model to predict the evolution of the flood and ebb channel. They suggest that the cell will remain stable if dredging-dumping activities do not exceed a certain limit. Hibma et al. (2003) modelled successfully morphological cells with the process-based model Delft3D. This report investigates the stability of morphological cells in estuaries by comparing stability results of the process-based model Delft3D to the simplified model of Wang and Winterwerp (2001).Settings of Hibma et al. (2003) are used to generate an equilibrium state suitable for stability analysis. Sediment is then dumped continuously in the flood or ebb channel at various rates to assess stability. The cell geometry, flow and sediment transport characteristics are used to review the applicability of assumptions underlying the simplified model. Results of the two models are confronted to gain further insight into the cell behaviour. Results are applied to the Westerschelde estuary to discuss the safety of the current dredging-dumping strategy.The study shows that the behaviour of the cell can be described in terms of channel dominance. It suggests that the current dredging-dumping strategy in the Westerschelde is generally safe. It also highlights the need for more understanding and control of the outcome of a Delft3D simulation.
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