The mussel population in the Dutch Wadden Sea, especially in the Western parts, is currently under pressure. Hydrodynamic process influence intertidal mussel beds in two ways: on the one hand currents are responsible for the transfer of food and sediments towards the beds, on the other hand, large shear stresses from waves and currents are capable of eroding mussels from intertidal mussel beds. A previous study suggested that wave exposure is an important factor determining the suitability of an intertidal area to sustain a stable intertidal mussel bed. However, the actual shear stresses associated with wave forcing have not been studied in soft-sediment environments; most research has focused on the role of currents. In this thesis the wave induced, and current induced bed shear stresses were quantified. Wave induced bed shear are larger than those resulting from currents. They are caused by physical interaction of the wave orbital motion with the bed; wave breaking does not occur because of the small slope of the tidal flat. Current induced shear-stresses were small. However, they have a substantial effect on the total bed shear stress due to wave-current interaction. Waves lose energy as they propagate over an intertidal mussel bed as a result of increased bottom roughness of the mussel bed. Wave exposure of the seaward edge of the mussel bed is largest. Areas deeper inside the bed are protected from high wave induced bed shear stresses by this seaward edge. The seaward edge is vulnerable erosion by wave-action but it can, as observations show, also be damaged by ice-action. Both processes not only erode parts of the bed they also elevate parts of the mussel bed surrounding the eroded area. This increases the wave exposure of these areas, making these areas more susceptible to erosion. The break-up of broad band structures, commonly observed in intertidal mussel beds, by storms might also influence food availability and thereby the persistence of an intertidal mussel bed. Results reveal the occurrence of flow ...