Pascal Finaud-Guyot

University of Montpellier 2, 2009.

Supervisor: V. Guinot; co-supervision: C. Delenne.

(ORCID); theses.fr/2009MON20142.

“Macroscopic flood modelling : Taking into account directional flows and main channel - floodplain transfer”

Abstract One-dimensional approaches prove to be efficient in river flow modelling as long as overbank flow can be neglected. When such approximation cannot be made, one-dimensional cell-based or two-dimensional models are used. However, in the first case, the momentum transfer, essential to a correct representation of phenomena such as meander shortcuts, is neglected. For 2D river flow modelling, a precise meshing of the river bed is required to correctly take the topography into account. The mesh close to the river bed is therefore composed of small cells and the simulation timestep has to be reduced to insure the numerical scheme stability. An alternative approach consists in coupling 1D and 2D models. Existing 1D-2D models prove not to be satisfactory in the general case, since only mass transfer are taken into account, neglecting momentum transfer. In the proposed approach, the coupling is performed by including a 1D model into the 2D model and providing a full transfer of both mass and momentum. This formalism allows for drastic reduction in the number of cells in comparison with a 2D meshing, and thus a substantial reduction of computation time. Numerical test cases as well as real-world application examples have been carried out for both a classical 2D and the proposed 1D-2D approaches. The proposed approach correctly represents the head loss due to channel bends as well as meandering shortcuts phenomena and provides good enough results for engineering applications with a reduced computational time. This is therefore a substantial improvement compared to both classical 1D and 2D models