Estuaries belong to the most developed areas in many countries. They are under severe stress, as the surrounding land is often densely populated and a concentration of industry, harbour activities and ship traffic is encountered. Many other commercial activities take place, such as fishing, recreation, sand mining, dumping of dredging material, disposal of industrial and domestic waste, etc. On the other hand, estuaries are important natural areas for wildlife, nursery for fish. Often large wetlands are found in estuaries. Through their interaction with the sea, estuaries form an important part of large scale eco-systems.
In serving all these needs many conflicts of interest emerge in the management of estuaries. The managing authorities therefore have a need to weigh the various interests and to predict the consequences of managerial measures in the system. Managing authorities are confronted with progressively more conflicting interests, smaller budgets and more severe legislation. In many of the problems they encounter in estuaries and coastal zones, the transport and fate of cohesive sediment, contaminated or not, plays a key role. Thanks to new developments in numerical modelling and measuring techniques, it is apparent now that this transport and fate is governed in many situations by near bed concentrated mud suspensions. However, our physical understanding is yet insufficient to quantify these processes adequately and formulate them properly in mathematical models. As a result large uncertainties exist in any prediction or recommendation that is made with these mathematical tools. This means that presently it is not possible to improve the physical rationale to optimize managing strategies, the minimization of maintenance costs, nor the evaluation of measures for sustainable development.
An important tool in these evaluations is formed by mathematical models. The shortcomings of the present class of models is discussed in the state-of-the-art. The improvement of these models provides the authorities with means to improve their weighing process. More specific, the impact of a series of measures and interference with the system become better predictable.
The COSINUS project aims at an integration of our perception of various individual processes and of the individual process formulations, and the subsequent integrated validation, with special emphasis on major shortcoming in our understanding, i.e. on the behaviour of near bed concentrated suspensions. An important aspect of this work is related to the practical implications of implementing the various formulae in mathematical models. We believe that in spite of the enormous developments in computational power, it is not yet, nor in the near future, possible to incorporate all these formulae fully in the models, as they then become unpractical to run. Therefore additional studies are required to obtain convenient numerical codes and parameterizations of the physics.
This is a challenge, as it involves the quantification of the flocculation process and the bed structure, turbulence modelling beyond a state that is routine in civil engineering, the interaction between Newtonian and non-Newtonian viscous fluids and a poro-elastic medium, thixotropic effects, implementation of the derived formulations, or their parameterizations in global mathematical models suitable for engineering purpose, and last but not least, the measurements within relatively thin layers of high concentrated near bed suspensions.
The results of the proposed research will contribute to a better assessment of the environmental impact of human interference and regulation in estuaries and coastal zones, improving the modelling tools used for environmental management. The major socio-economic advantages of the COSINUS project consist of:
• A better assessment of the siltation patterns, both with respect to the quantities involved, and the spatial and temporal distributions, enables the authorities to optimize the lay-out and maintenance costs of fairways and harbour basins. At the end this implies lower operational costs of harbours, improving their competitive edge in relation to other ports elsewhere in the world.
• A better assessment of the turbidity levels and accumulation patterns of (contaminated) sediment allows the sustainable development of estuaries and coastal zones; typical examples are the restoration of wetlands and intertidal areas. This contributes to a healthier environment within the Community.
• The commercial institutes working together within this project will increase their competitive edge on the international consulting market through the technology step that will result from the proposed research.
Our major innovation will consist of the development of explicit, physically sound mathematical descriptions of the behaviour of concentrated benthic suspensions and its interaction with the bed and the water column, and efficient mathematical formulations to apply this knowledge in everyday advisory work.
The COSINUS project will yield the following innovations:
• Assessment and quantification of the role of concentrated near bed suspensions on the transport and fate of cohesive sediment in estuarine and coastal zones,
• A formulation of the flocculation process of cohesive sediment in a turbulent environment, and its role on the formation of concentrated near bed suspensions and the structure of the bed,
• An integrated model formulation describing the stress response of the video porno, the erosion and re-entrainment process as a function of cyclical loading (waves) and current,
• A unified formulation for the processes of sedimentation, consolidation, liquefaction, fluidization and deformation of the bed.
• Validation, and where necessary modification, of classical turbulence closure models for application in near bed high concentrated suspensions,
• Development of convenient numerical codes and parameterizations enabling engineering applications of the mathematical models, and
• Guidelines for the execution of laboratory and field experiments and procedures for collecting the optimum data set aimed at studying the occurrence and role of near-bed concentrated suspensions.