|Modelling currents and sediment transport phenomena in shelf seas and estuaries|
Fettweis, M. (1995). Modelling currents and sediment transport phenomena in shelf seas and estuaries. PhD Thesis. Katholieke Universiteit Leuven. Laboratorium voor Hydraulica: Leuven. xxxviii, 253 pp.
Estuaries; Modelling; Sediment transport; Shelf seas; Water currents; Marine
Numerical models are an important tool for describing and understanding hydrodynamic and transport processes in the marine and estuarine environment. The success of these models is due to the fact that they are based on physical laws which describe in detail the processes involved. Two aspects of modelling, which are closely related, are highlighted. The first one focusses on the numerical aspects, while the second deals with validating the models through intercomparison with other models or analytical solutions and through field measurements. A2.50 vertical plane ice-ocean model and a 3D barotropic ocean model has been developed which simulates the wind induced currents in high latitude seas. The models solve the hydrodynamic and ice dynamic equations using finte different techniques. Because the domain of integration is very often smaller than the ocean basin non physical boundaries have to be introduced. Numerically this means that an open boundary condition has to be implemented. The Orlanski and the Camerlengo-O'Brien open boundary conditions have been introduced in an existing 2D depth averaged hydrodynamic model and have been validated by applying the model to some well defined test cases. It was found that the Camerlengo and O'Brien condition gave the best results. The Camerlengo-O'Brien open boundary condition has been used to simulate the flow behind a backward facing step in a long channel with the downstream boundaries open in order to investigate the quality of the results as a function of the advection scheme (1st order upstream and 3rd order QUICK).
The 2.5D ocean model was validated by comparing the results to those of an other model and to an analytical solution. The 2.5D ice-ocean model was forced by a katabatic wind. It is shown that coastal polynyas can be formed by theses strong off coastal winds. The differences found between both model results have been summarized and explained.
The 2.5D model has been applied to an (idealized) ocean covered by an ice layer and deal with the behaviour of an ocean in the vicinity of an ice edge and a continental slope.
The second part is devoted to the study of mud transport in a part of the Scheldt estuary using field measurements and numerical models. The observations show the great variations in mud concentration found in the Scheldt estuary. The mud transport is simulated using a 2D and a 3D model. The 2D transport model is a Lagrangian model. The model has been validated by comparing the model results to the data obtained from a laboratory model. This experiment has shown that the model is able to reproduce qualitatively and quantitatively well the observations, but that the predictive capability of the model suffers from a good description and integration of the various physical processes which governs the mud transport. The 2D mud transport model has then been applied to a part of the Scheldt estuary. The results of the model have been compared to the results of two other mud transport models.
The 3D mud transport model and several observations have been used to the study the mud transport in an access channel. It is shown that the high mud deposition in the access channels is mainly due to the density gradients existing between the river and the access channel and in the vertical plane.