|A process-based sand-mud model|
van Ledden, M. (2002). A process-based sand-mud model, in: Winterwerp, J.C. et al. (Ed.) Fine sediment dynamics in the marine environment. Proceedings in Marine Science, 5: pp. 577-594
In: Winterwerp, J.C.; Kranenburg, C. (Ed.) (2002). Fine sediment dynamics in the marine environment. Proceedings in Marine Science, 5. Elsevier: Amsterdam. ISBN 0-444-51136-9. XV, 713 pp.
In: Proceedings in Marine Science. Elsevier: New York. ISSN 1568-2692; e-ISSN 2352-2860
sediment distribution; sand; mud; bed composition; numerical analysis; modelling
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Predicting the bed composition in estuaries and tidal lagoons is of great practical importance. At present however, horizontal and vertical bed composition variations are often neglected in sediment transport and morphological models. In this paper a process-based sand-mud model is proposed, the model behaviour is analysed and model results are compared to field measurements, In general, it can be concluded that with such a process-based model, governing time scales and dimensionless parameters can be derived which can significantly increase the physical understanding. Furthermore, an expression is derived for the equilibrium mud content at the bed surface when both deposition and erosion occur during the tidal period. In this expression, the settling velocity for mud, the mud concentration and the erosion rate form an important dimensionless parameter. For low parameter values (< 10), sharp transitions are to be expected between areas with a very low mud content and areas in which the mud content can vary between 0 and 100%. The existence of a sharp transition is confirmed by field data from the Westerschelde estuary (The Netherlands). Finally, model results suggest that a local hydrodynamic parameter is not very useful for predicting the mud content in areas exposed to relatively low bed shear stress. Apart from the local hydrodynamics, the local mud concentration, settling velocity, mixing properties of the bed and the sample depth determine the local mud content.