Flow Dynamics in Salt Marsh Channels

Salt marshes provide an important habitat for animals and food for fish, shellfish, birds and mammals. They also serve as a breeding ground and nursery for numerous species. The value of salt marshes lies in the benefits that it provides to the environment and to people: they have ecological, social and economic values. Salt marshes produce their own tidal regime. They store and release ocean water in a tidal cycle depending on their morphology and dynamics. We report a general tendency for asymmetric velocities and discharges in salt marsh channels. This is because the hydrodynamic response to a tidal impulse is delayed due to the propagation of the tidal wave on the salt marsh surface. We demonstrate the necessity to introduce into a static model (model that simulates discharges over a tidal cycle based on the continuity equation) a delay function, responsible for the delay observed. The function is linked to the distribution of residence time. We prove the utility of the delay function through simulations, as well as the fact that this function is not unique for every salt marsh, but is, indeed, influenced by the salt marsh topography. Different delay functions reconstructed from the topography are applied to our simulated discharge and velocity data. The discharge and velocity results show a very close agreement with those observed in the field. Despite its simplicity, the model is a clear improvement with respect to previous results.