The operational water level prediction method in the Netherlands is based on the decomposition of water level into the astronomical tides and the surge. While the astronomical components are analysed and predicted by using Harmonic Analysis, the surge is predicted by using numerical hydrodynamics model named Dutch Continental Shelf Model, DCSM. Using this approach the nonlinear interaction between the components is not well accomodated. Moreover, the performance of the system now seems to have reached...