ABSTRACT
Flood simulation models are essential to assess human, economic and financial impacts of flood inundation. Simulations may provide information on historic flooding but also are commonly used for flood damage prevention and flow regulation. With the need to improve modelling accuracy and to gain computational time, coupled modelling approaches where the 2D model of a floodplain is combined with the 1D open channel flow model are increasingly used.
A finite volume 1D-2D coupled model is presented in this work. Both models are built using a conservative upwind cell-centered formulation based on Roe Riemann solver across the edges. The topography is represented with cross sections for the 1D model and with DTM (Digital Terrain Model) in a triangular unstructured grid for the 2D model. The resulting element of discretization for the coupled model is analysed and two coupling strategies based on a mass conservation and a complete mass and momentum conservation are proposed in order to cover all possible flow situations. The formulation is presented in a general expression, covering both frontal and lateral coupling configurations with respect to the 1D model. The idea of a correct conservation philosophy is emphasized, taking into account the information which leaves out the 1D or 2D domains.
Some academic and realistic configurations, involving steady and unsteady flow scenarios are used as validation test cases. The numerical results achieved by the coupled 1D-2D numerical model are compared from those obtained by the fully 2D approach, in terms of time evolution of some probes located at the domain, flooding extension and longitudinal profiles. The computational gain achieved by the proposed 1D-2D coupled model is also estimated in all the test cases presented, analysing the results in terms of speed-up in comparison with a complete 2D model.
