Process-based modelling of tidal inlet dynamics - Evaluation of Frisian Inlet data

The Netherlands Centre for Coastal Research (NCK) is in the process of preparing a comprehensive, coherent research programme focusing on the dynamics of tidal inlet systems with emphasis on the multi-scale dynamic behaviour of the ebb-tidal delta. Ahead of that research programme, this definition study was initiated with the objective to assess the capabilities of process-based modelling of meso-scale behaviour of outer deltas. This study can be divided into three parts. First, an inventarisation and analysis of former process-based model studies, conducted with Delft3D, is made. This modelling system has evolved to the point where robust simulations can be performed at time-scales of several years (meso-scale), even in complex areas such as outer deltas of the Wadden Sea. However, this is still shorter than the typical period of the morphological cycle ofthese inlets, which is in the order of several decades (macro-scale). An important short-coming to overcome the insufficient knowledge is the lack of validation and calibration of the hydrodynamics and morphodynamics, using real data from coastal measurements. Therefore, the second part of this report considers a measurement campaign, which was carried out in the Frisian Inlet in the context of the Coastal Genesis Programme. An overview of the data is given. The relation between the measured sediment concentration, current and waves is determined according to the formulation of the bed shear stress of Bijker and the transport formulation of Soulby-Van Rijn. The differences in the results between the two formulas is not distinctive. In the last part a model of the Frisian Inlet was constructed, using Delft3D. The development ofthe sediment concentration during a tidal cycle in several observation points along a cross-section of the main channel was analysed. The water level and sediment concentrations in the observation points reasonably correspond to the measurements. For the currents considerable differences were found. Several sensitivity computations were made. Comparing to Bijker, the Soulsby-Van Rijn formula leads to more morphological activity in the inner delta and when waves are absent to larger transports. After calibration the model will be useful in further research of tidal inlet dynamics.Hydraulic EngineeringCivil Engineering and Geoscience