The expansion project of the ‘’Port de la Nautique’’ and the creation of adjacent new beaches on the ‘’Lac Léman’’ in Geneva is currently under survey. In the conceptual and study phase, numerical- and physicalscaled models have been exploited at the Ecole Polytechnique Fédérale de Lausanne (EPFL). The objectives are to analyze the courantology and the wave’s field inside the protected zone of the harbor and their influence on the stability of the new beaches. The numerical modeling is driven by two models at different scales. The large scale model provides the boundary conditions to the small one which is used to estimate the circulation of water in the new harbor and to predict the erosion and deposition processes inside the harbor and along the beaches. The physical model is built using distorted scale factors inside an experimental wave tank that covers the same area as the small numerical model. It aims to optimize the project and to confirm the numerical results concerning notably the wave heights inside the harbor and the sediment transportation processes all along the beaches. The results obtained by the complicity of the numerical and physical simulations helped to converge toward an optimal design locations, orientations, and types of the protective dikes of the port as well as the geometric configuration and number of groins and the choice of the suitable backfill grain size for the new beaches.