Effects of urban topographical features on drainage efficiency for pluvial flash flood occurrence

In urban environments, pluvial flooding is influenced by engineering factors, including flood protection infrastructure, building configurations, and drainage system performance, alongside natural topographical features and rainfall intensity. Through numerical simulations of flood dynamics in a large urban area, incorporating artificial modifications to terrain slope and building coverage, this study quantifies the impacts of terrain slope and building presence on drainage efficiency and the occurrence of pluvial flooding. The mitigating effects of building complexes on drainage performance are also analyzed. Street inlets in low-lying, flat areas demonstrate high drainage efficiency, which diminishes as terrain slope increases and becomes significantly constrained beyond a critical threshold. Hydrodynamic modeling identifies a terrain slope threshold where drainage efficiency declines abruptly, likely associated to the design discharge capacity of standard street inlets. Although no clear trend emerges for the influence of building coverage on drainage efficiency, dense building complexes slow floodwater propagation on urban surfaces, mitigating terrain slope-related drainage losses and stabilizing drainage performance against abrupt changes.