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Numerical modelling of morphological development in a managed realignment project : a case study of the Perkpolder project

Zhao, X. (2016) Numerical modelling of morphological development in a managed realignment project : a case study of the Perkpolder project.

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Abstract:The Perkpolder project is one of the building with nature projects which can be considered as a managed realignment project. It is located in the Western Scheldt, the Netherlands. Part of the dike was breached and new defence line was built further inland which creates an intertidal area. The artificial creeks were shaped inside the Perkpolder intertidal area before the breaching which results in a deep pond near the inlet and the terminals of the creeks was spread out the area. The currents at the inlet and the topography changes of the Perpolder intertidal area has been measured. The discharge through the inlet shows that the intertidal area is flood dominant. The flow fields indicates that the inflow and outflow due to the low water level outside is constrained by the bathymetry as the inlet channels lead the flow propagation. The large sedimentation has been found in the pond and along the creeks. However, a channel with less sedimentation appears in the pond. This is the results of high velocities during the inflow as can be observed from the flow fields. A concept model has been setup in the Delft3D with tides as the major driving force and multi-fraction sediment interaction. The tides are simulated by imposing corresponding water level boundary for downstream and the current from upstream. The interaction with multi-fraction sediment influences the erosion flux which is based on the cohesive or non-cohesive sediment behavior. The model has been calibrated with the measured velocity at the inlet and the measured sedimentation and erosion pattern in the Perkpolder. The model showed its ability at reproducing measured the velocity components with a NS score indicating a good model performance. Moreover, the model successfully simulates the major bed level changes inside the Perkpolder intertidal area. Based on the model results, the sedimentation inside the Perkpolder intertidal area is strongly related to the flow circulation. The circulation is formed due to the shape of the Perkpolder and the bathymetry. The circulation influence the sediment transport as the sediment is transported with circulation. A ‘S’ shape sediment transport circulation during the outflow has been observed. The circulations results in the pond to acting like a sediment sink. While the erosion happens mainly during the inflow as the high velocity during inflow results in high bed shear stress. This brings the sediment into suspension. Moreover, the influence of creeks and breach width has been studied. The creeks protect its surroundings as the erosion is constrained along the creeks. Without the creeks, sedimentation cannot be observed at the larger area near the inlet. While by varying the breach width, the difference in sedimentation and erosion pattern is relative small. However, with a widen breach, more sedimentation has been found in the pond. It is due to the sediment transport circulation during outflow is more focus on the pond. For managed realignment project which is aiming at creating intertidal area, the sedimentation is beneficial. Therefore, including creeks in the Perkpolder intertidal area is a smart design as the creeks results in sediment attracted in the area.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
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