Wave forcing over an intertidal mussel bed

The Mosselwad project studies the stability and opportunities for restoration of mussel beds in the Wadden Sea. In this context we seek to predict mussel bed stability with respect to hydrodynamic forcing. To make accurate predictions with models, field experiments are needed to determine relevant processes and to establish representative estimates for model parameters. These parameter values were determined by a six week campaign on a relatively young mussel bed in the Wadden Sea. During this period wave height, period, propagation velocity, dissipation and flow velocities were measured. From these measurements values for the total rate of energy dissipation and the rate of wave energy dissipation were estimated. Results show a large increase in measured bed shear stress over the mussel bed compared with the uncovered parts of the intertidal flat. This is caused by the large roughness of the mussels. The turbulent kinetic energy was high above the covered parts of the bed. From the dissipation rate of TKE values for the corresponding bed shear stress and roughness height were estimated. These estimates were subsequently applied to calibrate a wave model which was used to determine the spatial distribution of the wave forcing. Model results show that the bed shear stress decreases over the mussel bed but increases behind the bed. Furthermore, a model study on the situation before the mussel bed settled shows that a minimum in wave forcing coincides with the seaward edge of the bed. This suggests that the bed is currently located in the optimal location with respect to wave forcing.