Modeling anisotropy in free-surface overland and shallow inundation flows

Regular patterns, which are found in both natural and man-modified environments, are strongly interwoven with free-surface flows. Examples are ridge and slough landscapes, cultivated terrains with ditches and furrows, and urban areas, with many of them characterized by a marked anisotropy. Simulation of overland and shallow inundation flows in these contexts is complex and demanding, especially if very different spatial scales are involved. Anisotropic effects are introduced to cope with two-dimensional shallow water models and, particularly, with the subgrid modeling technique. Application to schematic test cases shows the key role played by anisotropy in shallow flows, and second, that anisotropy can be effectively captured by the subgrid model with low computational effort and preserving mesh-independentness. High-resolution model results are accurately reproduced on coarser meshes using one fiftieth of the original computational elements, with a speed-up of more than 20. The subgrid approach could serve in view of physically based, large-scale modeling of floodplain inundation processes, in irrigation science, and in high-resolution hydrodynamic-hydrological simulations at the basin scale.