Print Email Facebook Twitter Morphodynamics of Ameland Inlet: Medium-term Delft3D Modelling Title Morphodynamics of Ameland Inlet: Medium-term Delft3D Modelling Author Jiao, J. Contributor Wang, Z.B. (mentor) Faculty Civil Engineering and Geosciences Department Hydraulic Engineering Programme Hydraulic Engineering Date 2014-09-26 Abstract The Dutch Wadden Sea is consisting of 7 tidal inlet systems separated by sandy barrier islands. The general morphodynamics and hydrodynamics of tidal inlets are relatively well understood, but the detailed interactions remain a prominent research interest. In this study, process-based computer models are employed as a tool to investigate the medium term mechanisms of the Ameland Inlet. Ameland is selected as this inlet is fairly undisturbed from human intervention and the relative large morphodynamic changes are well-documented. The aim of this study is to improve existing Delft3D models of Ameland Inlet. The model used is based on Fockert (2008) and uses a ‘Mormerge’ approach to derive morphodynamic predictions over a 12 year time frame. The model-data comparison focusses on two key aspects. Firstly, channel stability is analyzed based on the measured bathymetry datasets from 1926 to 2011. This analysis shows that the morphodynamic changes over the last 22 years (1989-2011) are representative for the present-day developments. Over this time-frame, the main channel is relatively stable and experienced a lateral shift up to half channel width (about 500m) and a depth variation in the range of plus and minus 1 m. The volume changes are analyzed over a more recent bathymetry (1999-2011). During this timeframe the basin increased in volume (9.6 Million m3) and the ebb-tidal delta (including coast) lost 29.7 Million m3 of sediment. Through a rigorous sensitivity analysis the effects of the most important morphodynamic parameters: the morphological acceleration factor, bed-slope effects, sediment composition are investigated. The use of spatial varying bed sediment grain size, and the Van Rijn bed-roughness predictor for flow, is essential in controlling the depth (stabilizing) the main inlet channel. An important finding of this study was the effect of the island sediment transports on the inlet development. A sensitivity analysis of the SedTHr, minimum water depth for sediment computations, indicates that erosion of the island tips plays an important role in the formation of secondary inlet channels. Allowing more or less island tip erosion, results in the more or less pronounced formation of a secondary inlet channel. The size of this secondary channel starts to dominate the morphodynamic change of the inlet over longer time frames. The sensitivity of long-term morphodynamic change to the setting of SedThr indicates that the interaction of the adjacent barrier island with the inlet is very important. This interaction is poorly understood and it is recommended to study this in further detail. In addition, improvements in the model are made in the schematization of the model boundary conditions. A new morphological tide has been derived based on the principle of Latteux (1995). Sediment transport through selected (key) transects along the main channel are analyzed. Based on this analysis, seven morphological tides can be selected that show (approximately) equal skill in reproducing the sediment transport based on the full spring-neap cycle. As an additional step, the sediment transport through cross sections between two barriers and correlation factor between the sediment transport of spring-neap tide cycle and morphological tide are evaluated to derive the single, most optimum morphological tide. The final model is able to predict the erosion of the Bornrif (nearshore Ameland island), the sedimentation in the eastern ebb-tidal delta and along the Ameland coastline. But the magnitudes of them are 5 times lower than the measurement. For other areas, the model could not show identical morphological behavior with the measured data. The main problem is the tide overestimate the sediment transport from basin to offshore, lead to the sedimentation of the ebb-tidal delta. Subject Wadden SeaAmelandDelft3Dmorphodynamics To reference this document use: http://resolver.tudelft.nl/uuid:e3d05254-1291-4334-b044-033e367b81fe Embargo date 2014-09-26 Coordinates 53.438110, 5.590101 Part of collection Student theses Document type master thesis Rights (c) 2014 Jiao, J. Files PDF Mscthesis_jiao.pdf 35.42 MB Close viewer /islandora/object/uuid:e3d05254-1291-4334-b044-033e367b81fe/datastream/OBJ/view