Olivier Gourgue's PhD Thesis

A densely populated watershed and numerous industrial activities, especially around the port of Antwerp, are responsible for the Scheldt Estuary and River to be highly polluted. Water and sediment circulation are major processes contributing to the global dynamics of the various pollutions. The objective of this thesis is to develop a numerical tool in order to make possible simulations of those environmental issues.
The finite element technique enables the use of unstructured meshes, so that the spatial resolution can vary widely over the domain. In our implementation, in the scope of the SLIM (www.climate.be/slim) and TIMOTHY (www.climate.be/timothy) projects, we combine one-dimensional equations for rivers and two-dimensional equations for estuaries and seas. Nevertheless, the tidal river network, the estuary and the adjacent coastal zone are simulated in the same framework.
The Scheldt Estuary features large shallow areas that are periodically emerging at low tide. This phenomenon is a numerical challenge in estuarine modeling because the governing equations are intrinsically unable to deal with areas where the water thickness may become zero. A flux-limiting method has been developed, which modifies the discrete form of the governing equations, in order to prevent the water surface to go down where it is already very low.
The last contribution is the development of the sediment transport module. Its calibration pointed out the influence of suspended sediment concentration, salinity and biological activity on the flocculation processes, as the influence of the biological activity on the erodibility of bottom sediments. Our 1D-2D model, with a very competitive computer cost, appears to provide results as accurate as those from more complex, three-dimensional tools, traditionally deemed indispensable in sediment transport modeling. Our approach appears therefore to be very promising for long-term environmental simulations of the Scheldt.

Jury:
Professor E. DELEERSNIJDER (UCL) (Promotor)
Professor V. LEGAT (UCL) (Promotor)
Professor T. PARDOEN (UCL) (President)
Professor T. FICHEFET (UCL)
Professor E. DELHEZ (ULg)
Professor W. BAEYENS (VUB)
Professor M. ELSKENS (VUB)