Porosity Models for Large-Scale Urban Flood Modelling: a Review

In the context of large-scale urban flood modelling, porosity shallow-water models enable a con-siderable speed-up in computations, while preserving information on subgrid topography. Over the last two decades, major improvements have been brought to these models; but a single gen-erally accepted model formulation has not yet been reached. Instead, existing models vary in many respects. Some studies define porosity parameters at the scale of the computational cells or cell interfaces, while others treat the urban area as a continuum and introduce statistical-ly-defined porosity parameters. The porosity parameters are considered either isotropic or aniso-tropic, and depth-independent or depth-dependent. The underlying flow models are based either on the full shallow-water equations, or on approximations thereof, with various parametrizations of flow resistance. Here, we provide a review of the spectrum of porosity models developed so far for large scale urban flood modelling.