The hydrodynamics of tidal energy sites is generally characterized by rough seabed, as shown in Figure 1. Such configuration favours the formation of powerful turbulent flow structures that strongly affect both the performance, and the lifespan of the turbine installations. To optimize the placement of the turbines, the effect of turbulent flows has to be understood, thus requiring a detailed description of the physical processes of turbulence. As part of the THYMOTE project, a Large-Eddy-Simulation (LES) approach is being developed which aims at computing the unsteady aspect of turbulent flows. LES approaches dedicated to environmental free surface flows are nowadays gaining popularity thank to the increasing power of supercomputers. This paper presents the implementation of a LES approach into the TELEMAC-3D solver, a hydrodynamic free surface flow model included in the open TELEMACMASCARET suite of numerical solvers. The TELEMAC-3D model  originally includes a Reynolds Averaged Navier-Stokes (RANS) solver dedicated to the simulation of environmental flows. The implementaion of the LES method in TELEMAC-3D consists of adding turbulence models  to mimic the effect of smallest motion scales as well as including suitable schemes to reduce
numerical dissipation. The implementation of the LES approach to TELEMAC-3D is validated using experimental measurements of a flow above dunes . Future applications of the LES approach will deal with the characterization of currents at the tidal energy site named Raz Blanchard (which is also refered as Alderney Race). We expect that the LES will enable more
accurate representation of the real world turbulent phenomena, including inherent turbulence and complex processes of vortex shedding.