PREDICTION OF COHESIVE SEDIMENT TRANSPORT AND BEDDYNAMICS IN ESTUARIES AND COASTAL ZONES WITH INTEGRATEDNUMERICAL SIMULATION MODELS

摘要

Within the E.U. fourth framework programme a joint research programme has beencarried out between 1997 and 2000 on the ?Prediction of cohesive sediment transport andbed dynamics in estuaries and coastal zones with integrated numerical simulationmodels? (acronymn COSINUS).The objective of the research programme was to establish well validated physical andmathematical descriptions of the behavior and fate of concentrated near-bed suspensions(CBS or ?fluid mud?) and their interaction with the water and the sediment bed.Since there seemed to be a lack of experimental data on the role of flocculation andturbulence in the formation and erosion of mud beds and on the formation of CBS, anexperimental programme has been set up to obtain these data. It consisted of fieldmeasurements in the Tamar estuary (U.K.) on floc formation and laboratory experimentsat Delft, Oxford and Grenoble on the formation of mud beds and CBS and the influenceof floc structure and turbulence on these processes. The data have been stored in a database, which is accessible to the public.Different processes have been studied in detail: turbulence damping in sediment ladenflow; turbulence production due to internal waves in concentrated suspensions;flocculation; generation, properties and entrainment of CBS; bed strength developmentand erosion of mud beds.The detailed process models have been parameterized to obtain relatively simpleformulations which can be implemented into currently used 3D and 2DH engineeringsystem models.The performance of the improved system models has been tested by application of themodels to a schematic estuary for which 2DV solutions with the detailed research modelswere used as a reference. The models have been applied and tested in three real estuaries(Tamar in U.K., Loire in France and Weser in Germany).It is felt that great progress has been made in the physically based description of cohesivesediment dynamics with respect a.o. to the formulation of turbulence damping functions;the modelling of the rheology of a CBS, incl. Consolidation; the modelling of flocculationand the modelling of erosion and entrainment of CBS.Engineering software tools have been improved to enable better predictions of muddynamics for the benefit of estuarine an coastal managers.