Hydrodynamic of artificial wetlands at the outlet of urban catchment: complementarity of the systemic approach and computational fluid dynamics tools
Résumé
The hydraulic efficiency of a stormwater pond was evaluated by means of a tracer experiment performed
at constant flow-rate. The Residence Time Distribution (RTD) was computed allowing characterizing the
mean residence time distribution and the dispersion regime. However, such experiments may be difficult
to carry out due to operational constraints. In order to characterize hydraulic efficiency for different flow-
rates, it was decided to compute RTD using the results from a 3D Computational Fluid Dynamics (CFD)
model and a 2D model relying on shallow water equations. The RTD simulated with the 3D model
exhibited rather satisfying agreement with experimental data whereas 2D model did not. A better
description of the floating weir geometry could improve 3D simulation results. The quality of 2D model
results is hampered by the simplifying hypothesis of boundary conditions descriptions (especially the
outlet) by the important numerical diffusion introduced by the first order finite volume scheme used. This
work showed that a 3D CFD code could be used successfully to determine RTD in stormwater ponds. 2D
modelling showed an interesting potential but needs further improvements. Hydrodynamic simulation
results will be used in the future to determine the systemic models of the pond for varying flow rates.