ABSTRACT Graphical abstract illustrating how mesh topology affects flow redistribution and, consequently, water levels in an idealised urban layout. Urban flooding involves complex flow redistribution and energy dissipation mechanisms that are difficult to represent with depth-averaged models. This study examines how mesh discretisation influences their numerical representation using four steady-flow experiments representing idealised urban layouts. A mesh-sensitivity analysis is performed with a finite-volume shallow-water model by varying mesh type, resolution, and orientation. Results show that water-depth predictions and discharge partitioning in the streets depend on how energy dissipation is numerically represented. In aligned layouts, models usually fail to correctly represent the flow dynamics, resulting in strong mesh sensitivity and inaccurate flow redistribution unless appropriate mesh types and resolutions are used. In contrast, rotated layouts are dominated by inertia-driven flow redistribution, making the influence of mesh characteristics more limited. A hydraulic-power framework is introduced to quantify head losses in urban layouts, particularly at crossroads, and to highlight unresolved dissipation mechanisms. Finally, the efficiency of a resistance-based closure using a calibrated urban Strickler coefficient is evaluated. While it can improve global water-depth predictions at a lower computational cost, the calibrated parameter is highly case-dependent, limiting its physical meaning and transferability. Overall, this work provides guidance for mesh design and clarifies the limits of resistance calibration in 2D urban flood modelling.
Ryckmans et al. (Fri,) studied this question.