Effect of Urban Drainage Inlet and Building Treatment on Urban Waterlogging Simulation Under Different Storms

Waterlogging simulation is an important non-structural measure for flood-risk management; however, the heterogeneity of urban surfaces complicates reliable simulation. Urban drainage inlets and buildings strongly influence runoff routing, yet the effects of alternative modeling treatments remain uncertain. This study evaluated the impact of three inlet treatments and three building treatments on urban waterlogging simulation under different storms. Results show that (1) under rainfall pattern 1, the grate inlet produced 4–5.8% higher peak drainage discharge than curb-opening treatments, and point-scale water-level differences reached 0.49 m at hydraulically sensitive locations. Compared with the roof-to-drainage method, the roof-to-surface discharge method increased flood volume, flooded area, and average water depth by 43.5%, 21.3%, and 15.6%, respectively. (2) The effects of the two representation types responded differently to rainfall characteristics. Drainage inlet rankings were strongly rainfall-dependent: under rainfall pattern 2 at a 100-year return period, the hierarchy reversed, with the depressed curb-opening inlet slightly outperforming the grate inlet by 0.6%. By contrast, the building treatment methods (BTMs) ranking remained consistent across all rainfall scenarios, with the roof-to-surface discharge method producing the largest flood volume and extent regardless of rainfall pattern or return period. Overall, this study identifies urban drainage inlet and building representations as important sources of structural uncertainty, providing practical guidance for urban flood modeling and drainage planning.