Granular bed protections are a common measure to mitigate scour of the sand bed around hydraulic structures. In view of marching towards cost-effective solutions to tackle erosion-related problems, it is important to accurately predict the loads exerted on the bed and come up with the needed rock grading. To that end, a 3-D eddy resolving modelling technique could help in formulation of a new stability formula, based on extreme local flow conditions It is the aim of this thesis to build a hydrodynamic numerical tool, able to predict governing mechanisms in stone stability. Special attention is paid on the way of representing a rough boundary and predicting wall and free turbulence. That being said, a Wall-Modelled Large Eddy Simulation (WMLES) is suggested and is build using the open-source CFD toolbox OpenFOAM. Firstly, simple open channel flow case simulations are set-up, to evaluate the performance of rough wall functions in the LES environment. Secondly, a backwards facing step kind of flow from the experimental study of Jongeling et. al (2003) is simulated and the performance of the numerical model is evaluated based on the experimental results. Finally, the suitability of this method for the target applications of this study is discussed, including a comparison with previous numerical studies of this research area.

Since 2003 there is a cooperation between the Hydraulic Engineering department of Delft University of Technology and Bulgarian universities. The cooperation focusses on exchange of knowledge and the development of the coast in the area of Varna. Dutch and Bulgarian students get the possibility to gain experience in data collecting, processing and interpreting. Repeating this fieldwork every year in the same area will provide an overview of the coastal development in the Varna area. The students will act as consultants for local hotel owners at the Varna coast. Their work consists of measuring hydraulic aspects in the project area and making a rehabilitation plan for the St. Elias Marina. Data collection consist of inventory material near site, beach measurements, wave measurements, profile measurements, quarry analysis and a bathymetric survey. The rehabilitation plan contains the development of sub-areas in the St. Elias Marina like the peninsula, north beach, south beach and the breakwater.