Recent years have seen an increase in the intensity of extreme rainfalls and the frequency of floods caused by climate change. As a result, South Korea is facing an ever‐increasing risk of flooding due to typhoons in the summer season. In South Korea, since the implementation of the ‘Four Major Rivers Restoration Project’, a variety of eco‐friendly riverfront facilities, such as ecological parks as well as sports and recreation areas, have been constructed on floodplains. These riverfront facilities have a high risk of damage due to inundations during the rainy season. To perform hydraulic analysis and stability assessment of these facilities, accurate numerical modelling is necessary. First and foremost, it is crucial to address the dry/wet (DW) phenomena caused by rising and falling water levels. In this study, a two‐dimensional (2D) finite element model was developed and its applicability was checked against the results of various DW analyses. The developed 2D model was then applied to a natural river undergoing DW phenomena. In the validation test, the applied 2D model demonstrated a high correlation coefficient (R2 = 0.954). Subsequently, using the results of the model, we calculated four types of flood risk indexes and analysed their correlations to evaluate the stability of the riverside facilities.

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Since the cross-sectional shape of the Nakdong river is compound type, the water stage rises up to the top of the flood plane, as the flow discharge increases during the extreme rain storm in summer. The recent increase of rainfall intensity and flood frequency results in the immersions of parks and hydrophilic facilities located in the flood plain. Therefore it is necessary to analyze the hydraulic characteristics evolved by the extreme rain storm in the flood plain. The study reach ranging from the Gangjeong Goryeong Weir and the Dalseong Weir, where several hydraulic facilities are located along the channel, was selected and numerical simulations were conducted for 42 hours including the peak flood of the typhoon Sanba. The 2-D transient model, FaSTMECH was employed and the accuracy of the model was assessed by comparing the water level between the simulation results and the measured ones at a gauging station. It showed a high correlation with R 2 of 0.990, AME of 0.195, and RMSE of 0.252. In addition, the inundation time, the inundation depth, the inundation velocity, and the shear stress variation in the flood plain facilities were analyzed.

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