Modelling the effects of submerged breakwaters in a wave basin

Abstract

This report is the result of a master thesis ofthe author, student at Delft University ofTechnology, Faculty of Civil Engineering. In this report a simulation oftests with submerged breakwaters, parallel to the shoreline, in a wave basin, are carried out with the morphodynamic model Delft2D-MOR. This 2-dimensional horizontal model was developed by DELFT HYDRAULICS. The aim of this thesis is to find out whether and how this model is able to simulate these tests with submerged breakwaters, and to investigate the effects of these breakwaters on profile development. The conditions ofthe experiments are used as input for the model. One simulation without breakwaters and two simulations with different breakwater configurations are carried out. Comparison of model results with measurement data rom the experiments shows that the model is able to simulate some hydrodynamic and morphological processes induced by the submerged breakwaters. Wave heights in the vicinity ofthe obstacles are reduced because of wave dissipation over the breakwaters. Flow circulation patterns occur induced by water level gradients. Sediment is mainly transported from behind the breakwaters towards and through the gaps seaward. However, there are still quite some differences between model and experimental results. Large amounts of sediment are eroded near the shoreline and close behind the breakwaters, which was not measured during the experiments. Apparently inaccuracies in modelling appear at the boundary of sea and land (original dry points remain dry, bottom gradients are irrealistic large), and at the location of submerged breakwaters where the modelling ofwave behaviour is not adequate. Also problems with resolution of computational grid arise at the location of submerged breakwaters. A higher resolution is needed in order to compute realistic flow velocities close behind the submerged breakwaters. Obviously a lot ofwork has to be done to improve the 2DH model results such that it can be a useful tooI for modelling the effects of submerged breakwaters on a beach profile.