Investigation of distributed-porosity fields for urban flood modelling using single-porosity models

Porosity-based model rely on the assumption that an urban area can be compared to a porous medium, where the porosity is defined as the ratio between the actual area available to the flow, i.e. not occupied by buildings, and the total area of the considered urban environment. In classical single-porosity models, the resulting value of the porosity parameter is considered as constant and accounts essentially for the reduced water storage capacity and reduced space available for the flow. As a consequence, the source term involving the porosity parameter only accounts for a local head loss at the entrance and at the exit of the urban area. Therefore, the head losses occurring inside the urban area are accounted for using drag-type source terms. In the present work, we tested different definitions of the porosity parameter, showing the benefits of accounting for areas with distributed porosity based on the actual layout of buildings and streets. This formulation is still compatible with the basic idea of porosity-based model, i.e allowing for the use of coarse computational meshes instead of refined meshing of the urban area