Finite amplitude sand waves in shallow seas : modelling of spatial and temporal variations in offshorre sandwaves [Powerpoint Presentation]

Sand waves form a prominent regular pattern in the offshore seabeds of sandy shallow seas. A two dimensional vertical (2DV) flow and morphological simulation model describing the behaviour of these sand waves has been developed. The model contains the 2DV shallow water equations, with a free water surface and a general bed load formula. The water movement is coupled to the sediment transport equation with a seabed evolution equation. The spatial discretisation is performed by a spectral method based on Chebyshev polynomials. A fully implicit method is chosen for the discretisation in time. With this model we investigate the intermediate term behaviour of an observed sand wave field of the Dutch coast. Firstly, a stability analysis is performed to determine the initially most preferred modes. Secondly, the numerical simulation model is used to investigate the properties of the system during the evolution of the sand waves. Hereby, we find sand wave saturation for a height of about 10-30% of the water depth with an average time scale of about 15 years. The sand waves become asymmetrical in the vertical. The order of magnitudes found of the time and spatial scales coincide with the observations.