Modelling offshore sand wave evolution |
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| Authors: | AA Németh SJMH Hulscher RMJ Van Damme |
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| Institution: | 1. Witteveen + Bos Consulting Engineers, P.O. Box 233, 7400 AE Deventer, The Netherlands;2. Department of Civil Engineering, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands;3. Department of Applied Mathematics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands |
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| Abstract: | We present a two-dimensional vertical (2DV) flow and morphological numerical model describing the behaviour of offshore sand waves. 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 by a seabed evolution equation. Using this model, we investigate the evolution of sand waves in a marine environment. As a result, we find sand wave saturation for heights of 10–30% of the average water depth on a timescale of decades. The stabilization mechanism, causing sand waves to saturate, is found to be based on the balance between the shear stress at the seabed and the principle that sediment is transported more easily downhill than uphill. The migration rate of the sand waves decreases slightly during their evolution. For a unidirectional steady flow the sand waves become asymmetrical in the horizontal direction and for a unidirectional block current asymmetrical in the vertical. A sensitivity analysis showed the slope effect of the sediment transport plays an important role herein. Furthermore, the magnitude of the resistance at the seabed and the eddy viscosity influence both the timescale and height of sand waves. The order of magnitudes found of the time and spatial scales coincide with observations made in the southern bight of the North Sea, Japan and Spain. |
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| Keywords: | Numerical analysis Finite amplitude waves Sand waves Shelf seas |
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