Porous shallow water modelling in differential form: Computation of cell-based conveyance porosity fields in a real urban layout

In the framework of porosity models for urban floods, this work presents a method to compute the spatial distribution of the porosity parameters for a real urban district. Specifically, the method estimates the four parameters required by the differential, dual porosity formulation, in which an isotropic porosity accounts for the reduced storage volume due to buildings, and cell-based conveyance porosities are introduced in the momentum equations in tensor form to model anisotropic resistances and alterations in the flow direction. The algorithm evaluates the porosity parameters on a cell-by-cell basis and only resorting to geometrical information. The proposed method is tested by simulating the flooding of a real, complex urban district in Italy.