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 demand substantial computation, sometimes exceeding typical forecasting horizons. In contrast, low-complexity models, such as local inertial approximations, provide accurate results in subcritical flows but may exhibit limited skill 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 comprehensive spatio-temporal assessment of 2D local inertial modeling using three numerical schemes (original formulation, s-centered, and s-upwind) in a dam-break scenario on complex terrain. The HydroPol2D model is benchmarked against HEC-RAS 2D full momentum solver. We present one numerical validation study comparing the developed model with benchmark examples, and three real-world scenarios. The first two are located in São Paulo, Brazil: a detention pond with a 1 in 100-year inflow and a highly urbanized catchment with a 1 in 50-year hyetograph. The latter, located in Pernambuco State, Brazil, provides the first comprehensive assessment of local-inertial model performance for simulating an instantaneous dam-break scenario affecting a city of nearly 200,000 inhabitants. Model validation against the benchmark example yields exact results, as reported in the literature. Real-world test results demonstrate that the model accurately simulates internal boundary conditions, representing drainage infrastructure, with peak errors of less than 5% compared to HEC-RAS 2D. However, neglecting urban infrastructure leads to peakdischarge differences of up to 21% and major hydrograph mismatches, while roughly doubling computation time. 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 was 23 times faster than HEC-RAS 2D, making it well-suited for rapid simulation of dam breaks or to be used in ensemble forecasting systems, in addition to being capable of modeling urban drainage infrastructure, such as orifices, weirs, and pumps.