Stromingsberekeningen in het Friesche Zeegat

Abstract

The Friesche Zeegat area is situated in the northeast of the Netherlands and is a part of the Dutch Waddensea. The Friesche Zeegat area consists of the barrier Islands Ameland and Schiermonnikoog and a part of the Waddensea. Drainage occurs through tidal channels and the major tidal inlets. Seawards of the inlet, an ebb-tidal delta occurs. The ebb-tidal delta, the tidal inlet, the adjacent parts of the islands and the channels and shoals of the inlet system represent one dynamic entity. Developments in different parts are strongly related and are largely defined by the tidal prism. By the artificial closure of the Lauwersea in 1969, the tidal prism decreased with a third. Due to the closure, the ebb-tide delta was suddenly too large and started to erode. Also the main tidal channels were too deep relative to the decreased tidal prism. This system hasn't found a equilibrium until now. The main inlet system has greatly changed in these years. This reduction has made the wave influence much bigger on the morphology of the whole area. In this master thesis, current and water/eveIs in the Friesche Zeegat area for the nothwest storm of October 9, 1992 are simulated with the numerical model WAQUA. The simulations are validated with measured currents and waterlevels. The calculated currents and waterlevels are used as input in the wave model SWAN on 6:00, 9:00 and 12:00 am around high water. The Friesche Zeegat Model is being calibrated and a sensitivity analysis has been carried out for several parameters, which influence the water motion. The simulation model WAQUA is developed by Rijkswaterstaat, and is able to perform two-dimensional (horizontal) computations The field measurements are delivered by the RIKZ (National Institute for Coastal & Marine Management) in a very preliminary format. These field measurements are sorted, checked and compared with the calculations. The current measurements are also sorted for the database system DONAR of Rijkswaterstaat and in this format these measurements will be available for future users. The sensitivity study of the Friesche Zeegat Model demonstrates a dominant influence of the boundary conditions on the water movement in the whole area (especially Northsea boundaries). An new (more recent for the year 1992) digital elevation model has been constructed for the Friesche Zeegat Model to make more accurate calculations for the current fields. Many tidal flats appear in the Waddensea area of the model. The WAQUA model seem not able to simulate the flooding and drying procedure of several gridpoints in the process of the calculations. A solution has been found in using an altered calculation routine of solVing the continuity equation. This altered calculation routine increased the simulation time of the calculations with 30 percent.