Lateral coupling method for different one and two dimensional shallow-water solvers: application to the hydro-informatic Telemac-Mascaret system

We present a lateral coupling method between one-dimensional (1D) and two-dimensional (2D) shallow-water solvers dedicated to numerical simulation of river overflows. Both 1D and 2D models, respectively in the river channel and in the floodplains, can be solved with implicit scheme in order to limit computational cost. The 1D-2D exchange terms for mass and momentum between the river and the floodplains are computed with an explicit solver of Riemann problem over a local area that extends over the coupling interface. A distinctive feature of the approach is its flexibility in reusing available computation codes of 1D and 2D shallow-water models as black-boxes. The proposed method has been implemented with the integrated suite of solvers Telemac-Mascaret together with the dynamical coupling software OpenPALM. Numerical validations with respect to an analytical solution and experimental data as well as a first application for the historical 1981 flood event over the Garonne River are presented. The results showed that the overflow discharge is well estimated by the coupled model while it tends to underestimate the water height near the lateral boundaries. For the real application case, reasonable agreement was found between the full 2D simulation and the coupled model.