Modelling Sand Wave Evolution and Migration in North Sea Using ROMS

Sand waves are large and transverse bed features, typically with lengths and heights of about 100-500 m and 2-10 m, respectively. The height can grow up to 30% of the average water depth, especially in shallow water conditions. Sand waves can migrate up to around 10 m/year and may profoundly impact subsea infrastructure, such as offshore pipelines and cables, key elements of offshore energy development. In this study, the evolution and migration of sand waves in the Dutch shoreface, North Sea 1986, was investigated using the Regional Oceanographic Modeling System (ROMS) and validated with DELFT3D and survey results from 2000. ROMS is an open-source oceanographic model available for free, created by the United States Geological Survey (USGS) to simulate ocean circulation, sediment transport, and seabed morphodynamics. Calibration of ROMS model conducted by modelling velocity profile in different location and free surface compared to field data. Validation ROMS and DELFT3D result was conducted by comparison the sandwave profile plotting in same graph. ROMS' simulation results agree with DELFT3D's results regarding horizontal grid size; vertical grid level; stretching parameters; time step; sediment diameter; M2 tide velocity which is the most dominant tidal constituent, representing the principal lunar semi-diurnal tide that has a period of approximately 12.42 hours and is caused by the gravitational pull of the Moon; M4 tide velocity which is the overtide of M2, generated by nonlinear interactions, especially in shallow water regions, a harmonic of M2 and has a period of approximately 6.21 hours (half the period of M2); net current in tidal; water depth; and waves. It can be concluded that horizontal grid size and stretching parameters are weakly sensitive to the results. In contrast, sediment diameter, M2 tide velocity, M4 tide velocity, net current in tidal, water depth, and waves may affect the migration significantly. Even though vertical grid level and time step parameters impact the results, these parameters need to be defined with a certain value following the Courant-Friedrichs-Lewy (CFL) condition.