  This article focuses on the numerical solution of the Diffusive Wave equation
posed in a domain containing a large number of polygonal perforations. These
numerous perforations represent structures in urban areas, and this problem is
used to model urban floods. This article relies on the work done in a previous
article by the same authors, in which we introduced low-dimensional coarse
approximation space for the linear Poisson equation based on a coarse polygonal
partitioning of the domain. Similarly to other multi-scale numerical methods,
this coarse space is spanned by locally discrete harmonic basis functions. We
show that this coarse space also lends itself to the linearized Diffusive Wave
problem that is obtained at each iteration of Newton's method. Furthermore, we
present nonlinear preconditioning techniques, including a Two-level RASPEN and
Two-step method, which can significantly reduce the number of iterations
compared to the traditional Newton's method. For all proposed methods, we
provide a discussion regarding the complexity of the algorithms. Numerical
examples illustrating the performance of the proposed methods include a
large-scale test case based on topographical data from the city of Nice.
