Spatio-temporal performance of 2D local inertial hydrodynamic models for urban drainage and dam-break applications

Accurate flood modeling is crucial for effective analysis and forecasting. Full momentum hydrodynamic models often require extensive computational time, sometimes exceeding the forecast horizon. In contrast, low-complexity models, like local-inertial approximations, provide accurate results in subcritical flows but may have limited skillfulness in supercritical conditions. This paper explores two main aspects: (i) the impact of urban infrastructure on 2D hydrodynamic modeling without detailed sewer and drainage data, and (ii) the accuracy of 2D local-inertial modeling using three numerical schemes (original formulation, s-centered, and s-upwind) in a dam-break scenario on complex, flat terrain. The HydroPol2D model is benchmarked against HEC-RAS 2D full momentum solver. We present one numerical case study and three real-world scenarios in S\~ao Paulo, Brazil: a detention pond with a $1$ in $100$-year inflow, a highly urbanized catchment with a $1$ in $50$-year hyetograph, and a dam-break scenario threatening a coastal city of nearly 200,000 residents. Results show that the model accurately simulates internal boundary conditions, achieving peak errors under 5\% compared to HEC-RAS 2D. However, neglecting urban infrastructure can lead to a 17.5\% difference in peak discharges at the outlet and significant mismatches in hydrographs, with computational times nearly doubling. The dam-break scenario demonstrates good predictive performance for maximum flood depths (CSI = $0.95$ for the original model, $0.92$ for s-centered, and $0.89$ for s-upwind), though the model's lack of convective inertia results in faster flood wave propagation than the full momentum solver. Notably, HydroPol2D is 23 times faster than HEC-RAS 2D, making it well-suited for simulating dam collapses in forecasting systems and capable of modeling urban drainage infrastructure such as orifices, weirs, and pumps.