The solution to many managerial problems in estuarine and coastal environments requires detailed information on sediment transport, turbidity levels and siltation rates. Examples are: wetland protection and restoration, the maintenance of navigation channels, dredging and dredged material relocation, the effects of construction works on siltation and turbidity maximum and the accumulation of contaminants. Mathematical models are the tools to obtain this information.
The models used at present, however, are unable to produce such information due to many simplifications.
Recent research shows that, in practical applications, the main shortcoming is the lack of understanding of near be processes in general and of concentrated near-bed suspensions of cohesive sediments in particular. These suspensions have the following properties: they can be non-Newtonian, damp turbulence and induce large transport due to gravity flow.
Starting from modelling experience, the major gaps in our understanding have been identified and the topics to fill these have been defined. In previous research the relevant physical processes have been studied separately, not in the field is the net result of the interaction of many processes. Therefore, the objective of the proposed research is to establish well validated physical and mathematical descriptions of the behaviour and fate of concentrated near-bed cohesive sediment suspensions and their interaction with the water column and bed.
Achieving this objective was not possible before as the necessary numerical tools, i.e. the integrated model (where "integrated" refers to the integration of all relevant physical processes over the entire water column and the sediment bed and their interactions), were not available. Progress in the understanding and the mathematical description of the various processes and in the increasing capacity of modern computers, opens new doors towards more sophisticated models. Only very recently a few of such integrated models, which allow the implementation of physically based process modules, have been developed and will be used in this project.
The following methodology will be applied: A study will be carried out of the interaction of the processes which play a crucial role in: the flocculation of sediment particles, the interaction between suspended sediment and turbulent flow, the generation and maintenance of concentrated near-bed suspensions and the transition between fluid mud and the sediment bed. New models will be set up and evaluated against experimental data. Available existing data will be used and, where necessary, new experiments will be carried out to provide the data to tune and validate the models. The models will be used to parameterize the process descriptions to implement them in existing system models. After testing, the improved system models will be applied to a few selected European estuaries to allow a quantitative assessment of the model performance. Experimental and numerical data will be stored in a data base. The work will be carried out in subtasks, to be executed by European universities and institutes which gained a thorough experience in cohesive sediment research.
At the end of the project the following deliverables will be produced:
- Well validated process modules and their parameterizations;
- A framework for integrated numerical simulations;
- Data base;
- Guidelines for field studies and survey specifications for assessing environmental management problems with a minimal data set.
Exploitation of the results is achieved through their implementation in advisory studies for managerial authorities.
Funding SchemeCSC - Cost-sharing contracts
OX10 8BA Wallingford
2600 MH Delft
2628 BL Delft
LL59 5EY Gwynedd
PL4 8AA Plymouth