Abstract: In this work, we study the proportions of different components of surface runoff on a community scale and their variations with different return periods of rainfall, using the GAST-SWMM coupled model and a case study of the Tianfu Heyuan community in Xixian New Area, and focusing on different simulation durations and different terrain boundary conditions. We find that this model, after validated against two measured rainfall events, gives the coefficient of determination of 0.83 and 0.82, indicating a high accuracy of the 1D-2D coupled model. Under the two scenarios of the community considered in this study, its surface runoff discharge rate and network drainage rate increase asymptotically with the increase in the rainfall return period, while the proportion of soil infiltration and the surface depression filling rate decrease. The surface runoff discharge and network drainage mainly occur in the rainfall periods, accounting for 94.88% and 94.36% of their respective annual totals. The impact of terrain boundary conditions in the community on its runoff process simulations is not negligible. The average rate of surface runoff discharge varies from 9.42% of the fence wall case to 22.55% of the no wall case. This study is useful for drainage and flood control in the areas relatively lower than the surrounding terrains.

Key words: urban flooding, runoff process, surface runoff outflow, zoning model, gradual curve