A study of urban flooding mitigation using PCSWMM and HEC-RAS 2D

Robson L. Pachaly and Jose G. Vasconcelos


There are strong indications that the number of heavy precipitation events will increase in the next years. Urban areas are more likely to experience social and economic damages caused by these extreme rain events than rural areas. Flooding is one of these problems, occurring when the collection system cannot properly convey the water that it is receiving. This is the case of an urban community located in the Southern United States that experienced recurring flooding events over the last years. Significant portions of its watershed have impervious areas and high slopes, leading to intense and short-duration peak flows. A modeling framework was proposed to represent the flooding areas and understand the mechanisms that led to flooding in the study area. The surface hydrology was simulated using a 1D PCSWMM model based on the Curve Number infiltration model and calibrated using field data obtained over various rain events. The flooding process was simulated using a 2D HEC RAS model. In this study, offline detention basins to mitigate flooding were also simulated using 2D HEC RAS by modifying the Digital Elevation model. The proposed approach predicted the flooded extension consistently with reported flooding. The conceptual design of the detention basin was shown to reduce the flooding extent, depth, and duration significantly for designing rainstorms based on synthetic hyetographs. The combination of PCSWMM and HEC-RAS 2D was a robust and accurate approach to evaluate the extent of flooding. Future studies will compare 2D flooding predictions yielded by PCSWMM with HEC-RAS 2D results.  

Keywords: PCSWMM, HEC RAS, flash flooding, hydrology. 

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