Numerical modeling of the tidal oyster mussel bed interactions with fine sediment in the Ems estuary

Oyster (in this research is the Pacific oyster i.e. Magallana gigas) mussel beds in tidal estuaries affect the sediment dynamics through increasing the sediment settling velocity (filtration rate) and decreasing the current energy by elevating the hydraulic bed roughness. Although an extensive research on the benthic organisms and their engineering works have been performed, detailed three dimensional (3D) numerical models which properly consider the oyster mussel bed interactions with fine sediment and include the ambient water properties (temperature, salinity and sediment concentration) are rare. To fill this knowledge gap and improve the available understandings on the interactions of oyster mussel beds with fine sediment, a 3D-Eulerian RANS model within the framework of an open source software i.e. Delft 3D-FLOW/MOR was developed to reproduce the hydrodynamic and corresponding morphodynamic results. The developed model is implemented for the Ems estuary and the adjacent German Wadden Sea using 21 vertical sigma layers and time frame of three months with a morphological factor of 12 (MF=12) to reproduce the morphodynamical developments of three years. The detailed model results for fine sediment (affected settling velocity, concentration, erosion and sedimentation) over an oyster mussel bed reveal the establishment of a high concentrated fine sediment layer and reduction of flow velocity compared with the model results without including the oyster mussel bed.