An efficient physics-based modeling strategy for pluvial floods in urban areas with a subgrid scheme for the stormwater drainage network

This study presents an efficient physics-based modeling strategy for simulating urban pluvial floods, which uses a subgrid approach to account for the contribution of (part of) underground drainage pipes. Coupled with a two-dimensional (2D) hydrodynamic model solving the porous version of the shallow water equations for the free-surface flow, the subgrid formulation allows running rain-on-grid (RoG) simulations while avoiding the time-consuming inclusion of the many small-scale components forming the stormwater network, such as one-dimensional (1D) pipes and storm drains. The proposed model accounts for the anisotropic additional conveyance provided by the stormwater drainage networks, assuming that the water level represents both the local free-surface elevation and the piezometric head for flow in pipes. Model parameters such as pipe direction, diameter, roughness, and spacing, can be derived from aerial images and limited surveys, thus reducing the data requirement and allowing for an easier model implementation than with classical dual-drainage models. Different applicative tests demonstrate that the use of the subgrid model ensures reasonable accuracy with low modelling effort and computational cost. The proposed approach offers an efficient and practical solution for pluvial flood assessment, particularly in data-limited and/or large-scale urban areas, providing support for flood management and mitigation strategies.