Author(s): D. Yu; S. N. Lane
Linked Author(s):
Keywords: Flood inundation modelling; Coupling; Diffusion-based model
Abstract: This paper describes the coupling of a 2D diffusion-based flood inundation model to a 1D river flow model and its application to an urban site across the City of York, on the River Ouse, UK. The 1D river model solves the full one-dimensional St. Venant equations for unsteady flow using the Preissmann Scheme. Two coupling approaches were investigated: (i) a loosely coupled approach where river flow is calculated before the 2D floodplain flow model is initialized and used as boundary condition to the 2D model at the river-floodplain interface; and (ii) a tightly coupled approach where 1D river flow is solved simultaneously with the 2D floodplain flow model by treating the flux exchange at the river-floodplain boundary explicitly through mass control at each time step. These two approaches were tested on a 10 km long river reach across the city centre of York. The 1D component of the model was validated against the recorded stage hydrograph upstream of the river and inundation extents were validated against the aerial imagery obtained during the flood event. The accuracy statistics shows that the tightly coupled model performs marginally better than the loosely coupled model in terms of the prediction of inundation extents. If the flow exchange between river and floodplain is not modelled correctly, it is likely that flood inundation extent will not be modelled correctly. This study emphasizes the importance of using correct boundary inflow conditions for flood inundation predictions. It is recognized that, the tightly coupled approach only accounts for the mass transfer between the floodplain and river channel. However, over-bank flow typically has two-dimensional (2D) and even three-dimensional (3D) characteristics. It has been found that flow routing at the river-floodplain interface is highly complex and may involve developments of strongly turbulent and three-dimensional flow fields. Thus, there are needs to model the momentum transfer processes at this boundary.
Year: 2007