Numerical modelling of the impact of drainage system clogging on urban flood processes

Drainage systems are an important infrastructure for reducing the degree of urban flooding, and clogging of street inlets or pipes is one of the important factors to influence the urban drainage capacity. Therefore, it is necessary to investigate the effect of drainage system clogging on urban flood processes. This study proposed a coupled 1D/2D hydrodynamic model to comprehensively analyze the response mechanisms of urban flooding to varying degrees and locations of drainage system clogging. First, the hydrodynamic model was constructed by integrating the 1D pipe network module of Storm Water Management Model (SWMM) with the 2D surface runoff module. Then the model was validated through a laboratory experiment of urban flooding in a typical urban street with drainage systems. Finally, the model was used for simulating urban floods in Qingshan district of Wuhan city, and the impacts of street inlet clogging and pipe clogging on urban flood processes were discussed. The results show that: (i) the model-predicted surface water levels and pipe discharges closely matched experimental results, with NSE values exceeding 0.92; (ii) with the increase in the rainfall return period, a significant increase was found in the inundation area, the number of surcharged pipes and surcharged junctions, and the underground pipe network would reach its maximum surcharge at an earlier time; (iii) both flood inundation area and inundation depth exhibited increasing trends due to the drainage system clogging, with flood severity rising proportionally to the clogging degree. Specifically, 14 % and 15 % of the study area showed an increase in the inundation depth of above 0.01 m under the scenarios of half-clogging street inlets and pipes, as compared with the unclogged scenario. Moreover, the zones severely influenced by the clogging of street inlets and pipes were mainly located in the regions with the surcharged pipes and junctions under the unclogged scenario. The results can provide the scientific basis for urban drainage system construction and flood risk management.