Modeling the influence of storms on sand wave formation: A linear stability

G.H.P. Campmans, P.C. Roos, H.J. de Vriend, and S.J.M.H. Hulscher

The North Sea is an area with lots of human activities. Next to shipping, pipelines and wind farms are installed at the sea floor. For safe operation in the relatively shallow North Sea it is of key importance to know the dynamics of the seabed. The seabed itself is far from flat and several rhythmic bed features can be observed. The most prominent features are sand waves: wavy patterns with hundreds of meters wavelength and a height of several meters. The tidal flow constantly moves sediment and leads to growth and migration of sand waves. The dynamic character of these sand waves interferes with human activities and requires surveying and dredging where necessary. Observational studies have suggested that storms may affect sand wave dynamics, but the mechanics had not yet been explained. A new study by WEM researchers extends insights into the dynamic behavior of sand waves in storm conditions. This behavior was studied through a novel process-based idealized sand wave model that uses linear stability analysis to investigate the effects of wind waves and wind-driven flow. The sand wave dynamics were compared for fair-weather (dominated by tidal flow) and for storm conditions (including wind waves or wind-driven flow). The results showed that wind waves and wind-driven flow indeed affect sand wave dynamics, and that these processes reduced the sand wave growth rate. Furthermore, the addition of wind-driven flow results in an asymmetric flow, which causes sand wave migration. Wind waves did not induce migration, but they were capable of enhancing migration induced by other processes, such as wind-driven flow.
The full paper was published in Continental Shelf Research
Published 7th February, 2017