Abstract: Along with rapid urbanization, imperious ground surfaces are expanding dramatically in China, resulting in a higher risk of urban flooding. This study focuses on accurate high-resolution simulations of rainfall-runoff process over an urban area featured with buildings, roads, grass lands and street outlets, and examines the performance of its surface drainage system. A two-dimensional hydrodynamic model is used in a case study of the Tsinghua University campus in Beijing, and it is calibrated and validated against the pressure gauge measurements of water depth at two waterlogging sites under two heavy downpour events. The results show accurate predictions of the surface flooding water depth and the necessity of using atmospheric pressure data recorded during the downpours to reduce the errors in water depth calculations that are otherwise significant. A detailed examination on overland flow patterns under a downpour of July 21st, 2012 reveals significant variations in the total runoff drainage into all the street outlets with different rainfall processes. Most of the surface impoundment was drained into rainwater outlets and 70.0% of the total rainfall volume released through surface runoff into the drainage system, while only 11.1% was through surface infiltration.

Key words: hydrodynamic model, surface waterlogging, high-resolution simulation, water depth measurement, atmospheric pressure