Long-term process-based morphological modeling of large tidal basins

The morphology of tidal basins includes a wide range of features developing along different spatial and temporal scales. Examples are shoals, channels, banks, dunes and ripples. Coastal engineers use their engineering tools to answer questions on the processes governing the short term ( centuries). This two-sided approach has left us with limited understanding of processes occurring on intermediate scales (> decades and < centuries), whereas the morphodynamics of these intermediate scales are of special concern to sustainable coastal zone management. This study is part of a collective effort to bridge the aforementioned gap by extending the use of coastal engineering tools (process-based models) to geological time scales to provide more understanding of the physical processes governing the long-term morphodynamic behavior of tidal basins. A fundamental question addressed is whether or not process-based models can reproduce trustworthy long-term developments. To answer this question the Dutch Waddenzee is chosen as a reference case. This study suggests that the question has a positive answer. By comparing model results with measured developments in the Waddenzee, this study shows that a process-based model can reproduce channel-shoal patterns and their long-term development qualitatively well. Modeled parameters such as area, volume and height of the inter-tidal flats obey the databased equilibrium equations. This study also demonstrates the models' ability to qualitatively assess the impact of large scale human intervention in a tidal basin. For example, the model is able to reproduce the change in tidal transport regime and the ensuing morphodynamic changes due to an extreme impact such as the closure of the Zuiderzee. Although the highly schematized simulations produced qualitatively good results, they also revealed the need for a better process description. As the first step to improve model performance a methodology was developed to account for sediment composition and distribution in the bed. In the next step different methodologies to schematize wave action for long-term morphological simulations were investigated. investigated the wave climate. Model results show that the chronology of wave conditions and the wave schematization approach have a limited effect. The outcome of long-term morphodynamic simulations with different wave and tidal conditions are in good agreement with conceptual models. For the reference case, model results revealed that the morphological impact of wind waves is not only important outside the inlet and at the ebb-tidal delta, but also within the tidal basin. A final conclusion is that adding methodologies for bed composition and wave schematization to the model of the Waddenzee area improved the hindcasting simulations qualitatively.Hydraulic EngineeringCivil Engineering and Geoscience