Interaction of Wind-Waves and Currents in the Ems-Dollard Estuary

Physical processes in coastal waters and estuaries extend their influences on many economic and ecological processes in the coastal regions and affect the safety of the coastal defences. In a context with the global climate change, these physical processes underlie also inherent modifications. In order to win an impression of such future changes and of the probability of their occurrence, physically consistent simulations of these processes are used to describe how wind-waves and currents interact. This paper presents an offline-coupled simulation using the models HAMSOM (HAMburg Shelf Ocean Model) and SWAN (Simulating Waves Nearshore). These state-of-the-art models excel by high computing speed, so that they offer an opportunity to simulate hydrological conditions and physical processes over longer time periods, e.g. decades. For the influence of currents on the waves, we estimate less influence on tidal flats, but stronger influence in the tidal channels. Improvements in parameter estimation that were achieved by the interaction of currents and waves are described and discussed; we estimate new drag-coefficients for the hydrodynamic simulation. Because long-term simulations need to be simplified, a method is examined and presented that by-passes the direct online-coupling of models. For the aim of long term simulation improvements of the surface drag coefficient are useful, because online-coupled wind-wave models overcome the available machine time for climate runs. Our method yields an optimization regarding computing economy and physical consistency of simulations