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Modelling cohesive sediment tranport in estuaries and coastal waters

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English title: Modelling cohesive sediment tranport in estuaries and coastal waters
Period: 1994
Status: Completed

Thesaurus terms: Modelling; Sediment transport

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Abstract:
The movement of cohesive sediments in estuaries and coastal waters creates a wide range of engineering and environmental problems. These problems include the erosion and sedimentation of estuarine navigation channels, harbours and waterways which largely affect the operation of harbours and the planning of maintenance dredging etc. In addition, the cohesive sediment particles generally act as the major carriers in transporting many chemical constituents into estaries and leads to the degradation of the quality of water used for consumption or recreational
purposes. The understanding of thes problems and their quantification for engineering purposes can be accomplished by modelling the movement of cohesive sediments in estuarine waters. In recent years, there has been a growing interest fornumerical models which can simulate the behaviour of fine, cohesive sedments in
estuaries and coastal waters. Numerical models can provide valuable and extensive information for hydraulic and coastal engineers involved in the management of harbours, estuaries and coastal regions. A finite element transport model was develop distribution of fine, cohesive sediments and bed level changes in estuaries and coastal waters. The 2D, depth-averaged, advection-dispersion equation has been solved with an appropriate sink/source term representing the sediment exchange processes at the bed. the proposed model is aimed at well-mixed estuaries. The
sediment processes such as, erosion, settling and deposition, have been incorporated in the proposed model through appropriate empirical relationshipsbased on laboratory and field investigations. The sediment bed was considered as composed of a number of layers, each having different values for sediment parameters. The model was verified using experimental data from annular flume studies. the results of 2 laboratory tests have been utilized which include the cohesive sediment transport in an annular flume under uniform and alternating currents. This work was undertaken as part of the MAST-2, G8 Coastal Morphodynamics research programme which was funded by the Commision of the European Community. The model was applied to a part of the Western Scheldt estuary to simulate the movement of cohesive sediments and deposition patterns. The model results are presented and discussed in detail. The model predictions have also been compared with two other transport models.

The complete sediment transport model is composed of three major submodels which relate to hydrodynamics, sediment tranport and bed level computations. As a result, the number of computations to be performed during model simulations are expected to be considerably high, so that large scale simulations are difficult to perform within a reasonable time. In order to improve the computational performance, the applicability of parallel computers for simulating sediment transport problems, was investigated. The proposed model has been implemented on the
iPSC/2 hypercube multiprocessor by utilizing domain decompostion techniques. Computational performances of the parallel implementation have been evaluated by a large simulation.

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